Toyota, which some consumers may believe is immune to a poor economy and the ills that other car companies suffer, actually is experiencing the same maladies that plague its competition.

For five straight months, Toyota Motor Sales U.S.A. has reported falling sales. In April, it reported sales of 217,700, a 4.5 percent drop compared with last April. Breaking down those U.S. sales figures by its two divisions, Lexus fared worst, with April sales of 23,350 units, a 17.1 percent drop from April 2007. The Toyota division sold 194,350 units, a 2.7 percent drop from last April.

The April results followed U.S. sales declines of 10.3 percent for March, 2.8 percent in February, 2.3 percent in January and 1.7 percent in December, according to Automotive News Data Center.

"Toyota has been so successful for so long that a lot of people expect them to be absolutely bulletproof," said Jack Nerad, editorial director of Kelley Blue Book. "They are a large company competing in the vast majority of the automobile market segments out there. They are operating at a scale that leaves them more vulnerable in some ways than a smaller company that doesn't have all of those volume targets that it has to match -- or all that capacity at plants to fill."

"The whole industry is suffering from the economy right now, and Toyota is no exception. While hybrids and small cars are doing well, our bigger trucks and SUVs are not," Toyota spokesman Wade Hoyt said.

Toyota's inventory of unsold cars and trucks is larger than ever before in its history, according to the Automotive News Data Center, with about 376,000 units unsold. That amounts to a 51-day supply for Toyota and Scion.

"I think they probably moved a bit too quickly in the U.S. to expand [plant] capacity," said Tom Libby, senior director of industry analysis for the J.D. Power Information Network. "I think if I was Toyota I would slow down my assembly plant growth in the U.S. and grow it more in my global markets."

"We still feel the market will come back eventually, so our plants will be able to work at capacity," Mr. Hoyt said. "The Tundra plants in Indiana and Texas have dialed back production somewhat, but on some of our most popular cars, like the Camry, we still have to import some of them, even though we build most of them in Kentucky."

Despite its recent problems, Toyota still is doing better than most of the auto industry. The company is gaining market share. In the first quarter it had 16 percent of the market, up from 15.6 percent at the same time last year.

"If I were them … I'd keep doing just what they are doing now," Mr. Libby said. "They are a believer in continuous improvements in their products, and they take little steps on an ongoing basis. I think they will be OK if they keep doing that. It's a way of staying ahead of the competition to practice this strategy of continuous improvement."

Perhaps most importantly, Toyota's product mix continues to be a source of strength. It is one of the few automakers with no perceivable market gaps or niches left unfilled.

"I think in general, their product portfolio is very good, and they are in parts of the market where they need to be. They lead the way in hybrids and crossovers, though they are struggling with Sequoia and Tundra because those segments are doing very, very badly overall," Mr. Libby said. "And as gas prices head higher, they are positioned well, with products at the lower end."

If Toyota has any problem at all with its product mix, "it's possible they have too many products in some segments," Mr. Libby said. "I think Toyota is having some issues with customers coming in to look for a smaller car, and the customer is experiencing some confusion about what they have to offer."

"Having various cars to offer in a segment isn't bad for the consumer, at least not on the face of it. And they need small cars to balance their Corporate Average Fuel Economy standards," Mr. Nerad said.

Equally important, Toyota can move more quickly than most other automakers to respond to market shifts and introduce new products or redesign older ones.

"They are helped quite a bit by their almost religious discipline of replacing cars every five years (six or seven years for trucks). If you do that, you never have any older products in your lineup that are just languishing," Mr. Libby said. That's a problem that some domestics and other foreign companies have, industry experts say.

Still, Toyota faces challenges that it rarely has had to deal with in the past.

For instance, quality always has been a hallmark of the brand. Yet this year, they have taken a big hit from Consumer Reports, a magazine frequently consulted by car buyers before they make decisions on their vehicles. The magazine dropped V-6 versions of the Camry from its "Recommended" list.

"We believe that we will have to earn back the 'Recommended' designation as Consumer Reports continues to do quality surveys," Mr. Hoyt said. "We are having fewer recalls than we had in the past, and our warranty claims are also down. So we believe that we are getting better, and we certainly hope that Consumer Reports sees that down the road."

"Quality is equalizing so quickly among auto companies that the issue of quality will eventually lose its power to help consumers differentiate among brands," Mr. Libby said.

U.S. brands, as well as archrival Nissan, are starting to run neck and neck with comparable Toyota products in quality.

Chevy's new Malibu, for example, has frequently been judged by auto writers to be equal to or better than the Camry in many ways. The same is true of Ford's Fusion. And Nissan's Altima outshone the Camry and many other intermediate family sedans in exhaustive testing done by Consumer Reports, which labeled the car its top choice in that category.

Toyota's edge in spending less money to get products to the market than its competition is diminishing too, auto industry observers say.

"The corporate costs structures for domestics are becoming much more competitive because of the recent round of new United Auto Workers contracts that will enable the auto companies to have cost structures that are much more in line with Asian companies," Mr. Libby said.