What Ray Catalano wants to know is: Why did the same prescription cost him $46 at one pharmacy and $557 at another? And why doesn't his insurer -- which ultimately pays 80 percent of the bill -- seem to care?

Mr. Catalano, a retired California University of Pennsylvania biology and environmental sciences professor, paid $557 in December at Rite Aid in Canonsburg for a month's supply of Zofran, an anti-nausea drug, following his hospitalization for a heart attack.

Prices can fluctuate. Last week, the price was listed at $543.99 on Rite Aid's Web site for the four-milligram tablets, and company officials say the cash price was $459.99 a few days ago.

Still, Mr. Catalano's prescription plan requires him to pay for medications upfront; he's reimbursed for all but 20 percent of the cost about three weeks later. Fronting $450 to $550 every month would be daunting for most people. On a retiree's income, Mr. Catalano said simply, "I can't do it."

So he shopped around and was surprised at what he learned: CVS was charging about $420 for 30 four-milligram generic Zofran tablets; Walgreens' cost was $410; and Wal-Mart charged $110.

Then he tried Jeffreys Drug Store, an independent pharmacy in Canonsburg. The cost to fill his generic Zofran prescription at Jeffreys: $46.58.

It's not just Jeffreys -- Bob Panconi, a pharmacist who works at an independent pharmacy near Steubenville, Ohio, says at least two generic pharmaceutical wholesalers offer pharmacies 30 four-milligram tablets of generic Zofran for less than $17, and his pharmacy probably would charge about $30. Calls to the two pharmaceutical wholesaler, Caraco and West-Ward, to verify those prices were not returned.

"I have no idea" why there is such a wide variation in pricing, Mr. Panconi said.

"I could see it if the generic just came out and they didn't adjust their computers for a month or two. But in this day and age with computers, even that doesn't seem acceptable."

The price difference also is a surprise to Lee Rucker, a strategic policy adviser for AARP. While AARP has not done a pricing analysis on prescription drugs, she said, chain stores typically can offer lower prices because they deal in bulk. "It is rare that you would get a better deal at an independent," she said.

The generic form of Zofran, called ondansetron, received FDA approval in December 2006.

More curious than angry, Mr. Catalano, 70, said he called a regional manager for Rite Aid who "could not give me a logical reason" for the price difference, he said. He also called his insurer, Highmark, and "it was almost as if they didn't want to hear it. They didn't want to be bothered. They said, 'That's not our job.'"

Michael Weinstein, spokesman for Highmark, said the possible variables of a particular plan make it difficult to know why prices may vary so much from pharmacy to pharmacy. "We can't dictate the price a pharmacy charges, any more than we can dictate what a hospital charges," he said.

Cheryl Slavinsky, spokeswoman for Rite Aid, said its pharmacies price competitively with other chain stores, although Wal-Mart can underprice all of them. She added that "we have no idea" how independents can offer generic Zofran so cheap.

"Most of our customers are insured, and they have a wide choice of pharmacies for prescription services, and so convenience, value-added services and days of operation, rather than price, are the primary drivers" of where customers choose to go.

It's true -- most customers, and many pharmacists, are unaware of a drug's real cost. People bring their prescriptions in, put their co-payments on the counter, then leave with their medicines.

Mr. Catalano said he would not have noticed either, if he hadn't had to pay upfront.

But once he knew, he wanted to find out why. Mr. Catalano called more stores, "probably seven or eight pharmacies around here. I called the major chains and a few smaller ones. I just couldn't keep quiet."

Mr. Catalano has corresponded with the state attorney general's office, too, which told him that prescription pricing is out of its jurisdiction unless there is evidence of deception or fraud.

"That's the thing that's very hard for me to fathom -- nobody will address the issue," he said.

So he has addressed it himself, telling his story in a public forum.

"I hope it serves to help others maybe save a buck or 500," he said. "If you don't shop, you get stuck with the corporate stores and they are all the same. They are all high."