Bristol-Myers officials also say the company won't use its patent on Zerit in South Africa, to block that country's efforts to buy less expensive versions of the drug from generic makers in India. In fact, Bristol-Myers is publicly acknowledging that it has almost no patent protection for its AIDS drugs in sub-Saharan Africa. It has a Zerit patent only in South Africa. And it has no patent for Videx in any sub-Saharan country. That means that right now, any nation or medical centre in the region could legally buy generic copies of those drugs if it chose to make such an effort.

Bristol-Myers's announcement follows an offer from Merck & Co. last week to sell two of its AIDS drugs at cost, or at about 45 per cent to 55 per cent less than the discounted price it offered last year. It also comes on the heels of significant price reductions by two Indian generic-drug makers."Our goal here is to energise a groundswell of action that needs to be undertaken if we are going to do any good in fighting this terrible problem in Africa," says John L McGoldrick, executive vice president of Bristol-Myers.

In recent weeks, activists have stepped up their pressure on drug companies to make AIDS drugs more affordable in the sub-Sahara, where 26 million of the world's 35 million HIV-infected people live.

Mr McGoldrick says his company is frustrated that a round of reduced price offers made by Bristol-Myers, Merck and three other drug companies last May hasn't yet had much impact in Africa. So far, only four countries - Rwanda, Ivory Coast, Uganda and Senegal - have accepted the new prices offered last year.

Bristol-Myers is taking the latest step, Mr McGoldrick says, because "We want to do our part." But, he adds: "African governments and donor governments in Europe, Japan and the US must join with the UN organisations, pharmaceutical companies, non-governmental organisations and others to address this human tragedy."

The Bristol-Myers executive echoed statements made last week by Merck officials. By bringing prices down about as low as they believe they can go, both companies hope to trigger a response by wealthy nations and others that might subsidise the costs of the drugs.

Even at the newly reduced prices, the drug therapy will remain far beyond the economic reach of most in Africa.

Bristol-Myers says that as part of its new proposal, it will sell Zerit and Videx for a combined price of $1 a day, or $365 a year. But those two drugs must still be combined with a third to complete the AIDS regimen. Merck's new reduced price for its drug Crixivan is $600 a year, and its new price for Stocrin is $500 a year. Adding either of those drugs to Bristol-Myers's two medicines will bring the annual price of a three-drug regimen in Africa to about $865 to $965. If, instead, Bristol-Myers's two drugs are combined with Viramune, a drug from Germany's Boehringer-Ingelheim GmbH that costs about $438 a year, the annual price of a three-drug combination will be $803.

Those prices are still slightly higher than an offer made in February by drug-maker Cipla Ltd of Mumbai, India, to sell a different combination of three AIDS drugs in Africa for $600. Suddenly, with the new round of price cuts from Merck, Bristol-Myers, Cipla and another Indian company, Hetero International Ltd., a pricing battle seems to be emerging in Africa. Indeed, Bristol-Myers's new price for Zerit undercuts by $16 a year the price Cipla is offering for its version of the same drug.

Some drug companies worry that selling at sharply reduced prices in Africa may lead to a black market for the drugs in the US. But Bristol-Myers says it isn't overly concerned about that at present.

In any case, it is unclear if the new prices will get to people in Africa quickly, or at all, unless employers and governments in the region and wealthy donors from abroad begin subsidising some of the drugs' costs. "It's pretty dramatic, a major, major step forward," says Harvard economist Jeffrey Sachs of the new price reductions. But Mr Sachs, who has been aggressively lobbying the US government and others to commit large resources to the AIDS problem in Africa, adds: "The limiting factor is international donor support to help buy these drugs at the discount and to provide training to make these drugs effective."