Two new studies released on Wednesday add to the growing body of evidence that taking a daily pill containing one or two AIDS drugs can keep an uninfected person from catching the fatal human immunodeficiency virus.

The studies were the first to show protection in heterosexuals; the only earlier one with similarly encouraging results involved gay men.

As it becomes ever clearer that modern antiretroviral drugs can not only treat the disease but prevent it, pressure is likely to increase on donors to find more money to supply them in places like Africa and on pharmaceutical manufacturers to either sell them cheaply or release their patents to companies that can.

“This is an extremely exciting day for H.I.V. prevention,” said Dr. Kevin Fenton, director of AIDS prevention at the Centers for Disease Control and Prevention in Atlanta. “It’s clear we’re not going to find a magic pill that prevents it, but this is adding more to the tool kit.”