The 45 million Americans who lack health insurance are one of the country's biggest social challenges. Lately, though, they've also become the insurance industry's hottest new growth market.

At a time when the traditional market of selling health insurance to employers is showing sluggish growth, insurers including UnitedHealth Group Inc., Aetna Inc. and the Blue Cross plans have begun to target uninsured people -- college students, part-time workers and even those with more comfortable incomes -- with lower-cost plans.

"We said there are (45) million people standing in the corner, and they represent potentially insureable people," says John W. Rowe, Aetna's chief executive.

The industry hasn't just discovered the uninsured, but it has realized in recent years that many of them are the same relatively healthy Americans they used to cover or administer to in employer health plans. As health-care costs continue to rise and more people lose company health benefits, few of them are turning to the conventional one-size-fits-all individual health plans.

It's one reason some of the industry's biggest leaders have taken stronger advocacy roles for the uninsured. UnitedHealth Group Inc.'s chief executive, William McGuire, has championed creating a set of basic health benefits for those without, while Dr. Rowe recently announced support for an individual health coverage requirement and providing some sort of assistance to those who can't afford it.

Taking their cue from retailers and consumer-products makers, insurers are segmenting the uninsured into specialized markets, then using many of the same market-research tools that go into developing new shampoos and snack foods. "The people who develop potato chips know just how crunchy the chip has to be and how much air to put in the bag, but we've been at a much cruder level in health care," says Andy Slavitt, managing director for UnitedHealth's newly created Center for Affordable Consumer Health. "We're thinking more like a retailer thinks."

What they have learned is that most people who weren't buying existing health-insurance products were dissuaded by their cost. For many people, the issue was more specifically that existing policies seemed to offer little value for the expense -- often because they required meeting such a high deductible before benefits kicked in. And many, particularly younger people or small-business owners, were put off by the complexity of trying to find the right plan.

Some of the new insurance plans are specifically targeted at those concerns. Last year, Blue Cross of California launched Tonik, a line of health insurance whose "Thrill-Seeker," "Calculated Risk-Taker," and "Part-time Daredevil" plans target uninsured twenty-somethings. Aetna has acquired companies that sell plans to college students and temporary and part-time workers. UnitedHealth -- and to a smaller extent, Humana Inc., and Cigna Corp. -- recently struck an agreement with 60 large employers to sell bargain-basement plans to as many as three million early retirees and part-time workers without company benefits.

These plans don't offer all the benefits of most employer-sponsored plans. While many of them cover catastrophic illnesses and include upfront coverage for a set number of doctor visits or some preventive services, they often have higher deductibles and more restrictions or exclusions of certain benefits, such as covering pregnancies. That worries some health-care experts.

"Maybe it's better to have some coverage rather than nothing," says Sara Collins, a senior program officer at the Commonwealth Fund, a health-care policy foundation in New York. "But are we setting up a system in which we have fewer uninsured but substantially more underinsured?"

Some experts consider youth-oriented products like Blue Cross's Tonik a step in a dangerous direction because, they say, their slick marketing glosses over the limitations in benefits. "They are specifically catering to an ignorant population that has little understanding about what insurance is and what it should do," says Ruth Haskins, an obstetrician-gynecologist who is legislative committee chairman for the California branch of the American College of Obstetricians and Gynecologists. She argues these plans skim off young, healthier people, making it even more expensive for sicker uninsured populations to get coverage. "So you have low-risk people with really crappy insurance and high-risk people who can't afford anything," Dr. Haskins says. "Is that any better?"

Others counter that even limited health insurance is a tremendous improvement over having no coverage at all. "One of the things we know about uninsurance is that it's bad for your health," says Dr. Rowe of Aetna. Those without insurance put off seeing doctors until a medical crisis, then usually have to go to the emergency room. Even with limited health insurance, "You get prevention and you get access," he says. To not provide a more affordable product because it falls short of complete coverage, "that would be the perfect driving out the good."

Here are some of the market niches where health insurers are targeting unconventional products:

Young adults

Those between ages 19 and 29 make up one-third of the uninsured. Because young people are relatively healthy and rarely see a doctor, many are put off by high premiums.

But being young and healthy is what makes them attractive to insurers. When Blue Cross of California set out to create Tonik, it asked dozens of uninsured people in their 20s to keep diaries of their health-care decisions over several months. "By watching them we could figure out the roadblocks," says David Helwig, president of WellPoint Inc.'s Western region, which includes Blue Cross of California.

One young woman showed them a six-inch stack of insurance information that she had avoided going through to make a decision. So Blue Cross designed a 15- to 20-minute online application process for Tonik, and is promoting it with images of snowboarders and hipster language.

Justin Doss, a 26-year-old computer consultant in Oxnard, Calif., recently went freelance and learned that insurance policies would cost him $200 to $300 a month. "For my age range, it was so high it just wasn't worth it," he says. Instead, he stopped riding his motorcycle and snowboarding, afraid of risking an accident. A friend mentioned Tonik and within an hour, he says, he was approved and able to print out his insurance card -- in time to make a snowboarding trip with friends he had planned to skip.

Tonik's monthly premiums range from $64 to $123 and members pay $30 copayments for doctor visits and certain medical tests included in the visit, but they have a high deductible of $1,500 to $5,000 for things such as hospital stays. And Tonik excludes maternity coverage.

Blue Cross of California says Tonik excludes services such as maternity because its focus groups of uninsured twenty-somethings were emphatic about not wanting to pay more for benefits they didn't need, and that the majority of its plans do offer maternity care for those who want it. About 70 percent of Tonic members came from the ranks of the uninsured, it adds.

Aetna, meanwhile, bought Boston-based Chickering Group in 2003 to sell student health plans to universities and colleges. Since 1998, Chickering's membership has more than doubled to 321,000, and with more than four million U.S. students still uninsured, Aetna says it sees big growth potential. While about 50 percent of college students remain covered by their parents' health-insurance plans through their college years, many insurance plans stop coverage for children once they reach 18 or 19.

In many cases, schools require students buy the insurance, usually for about $1,000 a year. Aetna keeps premiums low by capping coverage on some treatments, such as physical therapy or counseling, and requiring students to use the campus health-care clinic as their main provider.

Part-timers, temporary workers and early retirees

For employers, particularly in the retail and service sectors, that don't offer many traditional benefits, insurers are developing limited-benefit packages that can include coverage for some doctor visits, preventive care and catastrophic illness. These plans are also being offered to early retirees in lieu of traditional retiree health benefits.

In January, Aetna bought Strategic Resource Co., which administers limited-benefit health plans, to give employer clients an insurance option for uninsured workers. Employee premiums typically run $50 or $100 a month for a package of limited benefits. In some cases, employers subsidize the benefit, Aetna says.

UnitedHealth is also creating plans for the uninsured that draw on extensive consumer research. What came through loud and clear in focus groups, United's Mr. Slavitt says, was that people didn't see value in a plan with just a high deductible. So the plans cover items such as preventive health care, a certain number of doctor visits and a certain amount for prescriptions. In a handful of cases, the employer decided the plans were affordable enough that it subsidized them for employees who traditional didn't get any type of health coverage.

Mr. Slavitt says the company is also talking to employers about helping employees in their 40s and 50s set up and fund a special health-care account to be used after leaving the company. "It would be presented by the employer as a just-in-case," he says.

Middle Class

For the 15 percent of the uninsured who have incomes over $50,000, many insurers are hopeful that the new tax-advantaged Health Savings Accounts will make high-deductible plans more attractive. For example, Aetna began selling such plans on the individual insurance market in nine states over the past year.

Anthem, now part of WellPoint, launched its Blue Access Economy plan in January after holding extensive focus groups with middle-income uninsured. Again, it found that people didn't want just a high-deductible plan with limited benefits. So Anthem included three annual doctor visits, at a $30 copay each, and a generic drug plan (with a cap of $500). With a $1,000 deductible, the plan costs $62.97 monthly for a man in Ohio, about 25 percent less than the company's most popular individual health plan. Since the plan was launched in January in Kentucky, Ohio and Indiana, the company says it has signed up thousands of customers. About 45 percent of them were previously uninsured, and 99 percent were new customers altogether.

"That shows we're not just taking business away from our existing products," says Jude Thompson, head of the company's individual products in the three Midwestern states. "This is a whole new business opportunity."

When Steven Rowland of Greenwood, Ind., quit his full-time job last year to focus on his party equipment-rental business, he lost his company health benefits. But most of the individual insurance policies available to him cost about $300 a month. "Being self-employed, the cost of health insurance was just ridiculous," he says. "I was ready to gamble and just pray nothing happened (to his health)."

Then his insurance broker told him about WellPoint's Blue Access Economy Plan, with premiums that would cost only $120 a month. Since he's relatively healthy, the higher deductible doesn't bother him. His biggest health-care expense is an occasional doctor visit -- which is exempt from the deductible and costs just a $30 copay. "To me, it doesn't seem much different than the company plan I was on," he says.

Still, while insurers are emboldened by the growth in such products so far, it's unlikely they will put a great dent in the still-swelling ranks of the uninsured. Two-thirds of the uninsured -- and still the fastest-growing group -- are in low-income households, with money barely able to cover other basics such as rent and groceries. One-third of the uninsured live at or below the poverty line. "These groups have access to the individual market now, and it's not affordable," says Ms. Collins of the Commonwealth Fund. "You only have to look at the demographics to see (these products) are probably not going to have much of an impact."

Without a Net

Traits of the 44.7 million uninsured Americans in 2003:

Income

Two times federal poverty level(1) (FPL) or more -- 36 percent
Below FPL -- 35 percent
100-199 percent of FPL -- 30 percent

Family Work Status

One or more full-time workers -- 69 percent
Part-time workers -- 19 percent
No workers -- 12 percent
(1)The federal poverty level was $18,810 in 2003 for a family of 4.

Source: KCMU and Urban Institute analysis of the March 2004 Current Population Survey