In the first moments after Faniswa Butshingi learned that she was both pregnant and infected with HIV, she said she considered suicide. But that terrible day, a nurse handed her a reason for hope: a bottle of nevirapine.

The drug, used widely around the world, had generated controversy in South Africa that for years pitted AIDS activists against a government reluctant to distribute nevirapine. The result was a protracted court battle. Yet the instructions to Butshingi were simple: Take one pill when labor starts. A dose of nevirapine syrup would be given to her baby a few hours after birth. With any luck, the child would be spared from the virus that causes AIDS.

That was nearly two years ago. Today, at the same hospital, another nurse showed Butshingi, 24, a piece of paper revealing the news she had hoped for: Her plump and outwardly healthy 1-year-old son, Luthando, showed no signs of the virus in his blood.

Butshingi covered her face, then smiled down at her baby, who lay asleep in her arms, bundled against the cold June air. Like thousands of other babies born at the hospital in the past few years, he had escaped HIV, at least at this tender age.

"It's unbelievable. It's unbelievable. I am positive, but the baby comes out negative!" Butshingi said, wiping away tears. "He can grow and grow and grow and grow, thanks God."

Researchers say there are no reliable statistics on how many babies nevirapine has saved nationwide. But at Chris Hani Baragwanath Hospital -- the main source of prenatal and obstetric care for millions of people in Soweto, the sprawling township near Johannesburg -- 25 percent of babies born to HIV-positive women contracted the disease in the mid-1990s, before nevirapine became available. Now that the drug is administered routinely, the infection rate is about 8 percent, doctors say.

"It's your magic bullet," said Glenda Gray, director of the Perinatal HIV Research Unit at the hospital. "One pill to the mother, one pill to the baby, and you halve your transmission rates."

The government runs a $4 million program to prevent mother-to-child transmission in Gauteng province, which includes Johannesburg, Soweto and Pretoria, and four out of five pregnant women with HIV receive nevirapine. The test is considered reliable after a child's first birthday.

Some of these numbers were reported Tuesday in the Star, a Johannesburg daily. Nomonde Xundu, the province's director of HIV/AIDS, tuberculosis and sexually transmitted diseases, warned against extrapolating limited data to calculate how many babies had been saved from infection but agreed the news was good.

"The 8 percent is encouraging," she said, "but you need to be careful how you interpret it."

For years the South African government warned that nevirapine had dangerous side effects and could not be reliably administered without drastically improving the quality of care available at state-run hospitals.

The AIDS activist group Treatment Action Campaign filed a lawsuit against the government in 2001 demanding the distribution of nevirapine to HIV-positive pregnant women across the country. The court ruled in favor of providing the drug.

Since then, there has been little evidence of dangerous side effects from nevirapine, though there is evidence that use can create resistance to it and similar anti-HIV medicines. Researchers fear that women who use nevirapine during the births of their children will be resistant to other anti-retroviral drugs later, when they develop AIDS.

Chris Hani Baragwanath, which has nearly 3,000 beds and 5,000 employees, claims to be the largest acute care hospital in the world. It began using another anti-HIV drug, AZT, to curb mother-to-child transmission in the late 1990s and switched to nevirapine in 2000.

Among those who received the drug in that first year was Pertunia Matereke, 37, whose 4-year-old daughter, Lerato, later tested free of the virus. Like Butshingi, Matereke learned that she was infected with HIV only when she was tested during her pregnancy, two months before Lerato was born.

"I was given the results. I had to deal with the results, then I was told to bring back my daughter for a test," Matereke recalled.

After tests indicated that the baby was negative, "I was very much relieved, she said. "I couldn't handle the stress of being a positive mother with a positive baby. I couldn't cope."

Doctors at the hospital say that nevirapine is only the first step to successfully combating mother-to-child transmission. Surgical births help reduce infection rates, as does bottle feeding the child, because breast milk can contain the virus. And drug combinations may prove more effective than nevirapine alone, they say.

South Africa has the highest instance of HIV infection in the world, with estimates topping 5 million. Doctors at Chris Hani Baragwanath said that more than 25 percent of pregnant women in Soweto are infected, a rate even higher than national data on HIV prevalence among non-elderly South Africans.

"Saving thousands of babies in any other city in the world would be profound," Gray said, but in Soweto, "it's only a foot in the door."