The Internet appears to be a virtual meeting place for gay men willing to engage in high-risk sexual behaviors that often lead to transmission of the virus that causes AIDS, according to research presented here today.

Gay men who meet sexual partners online are more likely to engage in unprotected intercourse with them than they are with partners met elsewhere, according to a survey by researchers in New York. Furthermore, those already infected with the virus are more likely to have high-risk encounters with online partners than are people who are not infected.

"The Internet is a new venue associated with high-risk sex," Sabina Hirshfield, of the Medical and Health Research Association of New York City, told scientists at the 10th Retrovirus Conference, the annual midwinter AIDS conference held in the United States.

The Internet study was one of several presented here that sketched in details of the contemporary AIDS epidemic in the United States and provided possible new strategies for controlling it.

The researchers last summer recruited about 3,000 visitors to the Web site to answer a 60-question survey about their sexual practices over the previous six months. Men from all 50 states were represented, 85 percent were white, and nearly 90 percent had attended college for at least a while. About 8 percent were infected with human immunodeficiency virus (HIV).

Eighty-four percent said they had met sexual partners online.

Those men were slightly more likely to report unprotected anal intercourse (64 percent) in the previous six months than men who didn't meet partners online (58 percent). Significantly, however, the HIV-positive men who found partners on the Internet were more -- not less -- likely to report having unprotected intercourse than other men using the Internet for the same purpose.

Hirshfield told her listeners that the study suggests "it may be possible to reach high-risk [men] through Internet interventions."

Other hazardous encounters were examined in a study of HIV-positive inmates after their release from North Carolina prisons.

David Wohl and colleagues at the University of North Carolina interviewed about 90 such inmates -- roughly half men and half women -- before they finished their prison terms (in most cases, less than two years), and then two months later.

About half reported sexual activity soon after release, and 30 percent said it was unprotected sex with a longstanding partner who was either uninfected or whose HIV status was unknown. About one-third of the total group said they thought it was "likely" or "somewhat likely" that they would eventually infect their main partners.

Wohl and his colleagues had no data on whether any of the prisoners had become infected with HIV in prison. But only a handful reported having sex there, and in all cases it was consensual, he said.

He speculated that prisons' main role in the AIDS epidemic was not as sites where infection was acquired, but as places from where infected people prone to risky behaviors cycled in and out of the population. Intensive prevention efforts could be directed at them, he suggested.

Exactly when a sexual encounter between so-called "discordant" partners -- one infected, the other not -- is most hazardous was the subject of a report from a long-term study of men and women in the Rakai district of Uganda.

Extensive interviews with 443 discordant couples, along with regular HIV testing, led to the observation that the greatest risk of virus transmission was in the first five months after one person in the couple became infected.

During that period, the rate was 8.2 transmissions per 1,000 acts of coitus. Afterward, the rate fell to 1 transmission per 1,000 acts. In the year before an infected person's death, the rate rises again to 4.3 transmissions per 1,000 acts.

The findings lend support to the current campaign by the Centers for Disease Control and Prevention to encourage widespread HIV testing of Americans so that people can be counseled as soon after infection as possible, even if they do not begin antiretroviral treatment for years. About 900,000 people in the United States are believed to be HIV-infected, with about one-third unaware they are.