The average cost of bringing a new drug to market is $125 million. The maker of AZT, the Burroughs Wellcome Company of North Carolina, refuses to state its costs, but it's hard to believe they reached a fraction of this sum. AZT was first synthesized in 1964, as a possible anti-cancer agent, by Jerome Horwitz of the Michigan Cancer Foundation. In 1984, Samuel Broder of the National Cancer Institute encouraged companies to submit possible anti-AIDS drugs for screening by a special test developed in his laboratory. Burroughs Wellcome sent in AZT, a compound it happened to have on its shelves after studying it for another purpose.

Since few other pharmaceutical companies were much interested in AIDS drugs at that time, Burroughs deserves credit for pressing ahead. But to encourage it to take even this chance, the Government allowed it to apply for full patent rights, despite the heavy Federal contribution. The Government then conducted or supported many of the clinical tests of AZT, and for early production it provided all the thymidine, a critical ingredient.

Burroughs at first justified its astoundingly high price for AZT by noting rival drugs would soon be on the market. But the rival drugs still haven't appeared. Burroughs did reduce the retail price from $10,000 to $8,000 in 1987. The company now says the present 40,000 AIDS patients are the only customers it can be sure of. Every epidemiologist expects the toll to rise far higher.

As other promising AIDS drugs reach the market, competition will force the price of AZT down. But that may be many months ahead, and meanwhile Burroughs's apparent profit bears little evident relation to its risks.

Burroughs Wellcome is the subsidiary of a British company that is 75 percent owned by a charitable foundation, the Wellcome Trust. Wellcome's trustees are academics, many of them retired, who distribute the revenues for medical research. This is no doubt a worthy cause. But it's a strange kind of charity that cordons off people already suffering from a terrifying disease.