During the formative research phase, investigators will undertake formative studies to locate, understand, and characterize high-risk social networks of African American MSM in the community; gain community participation, involvement, and input; and undertake interviews with key informants and community members to gain information needed to pilot test study recruitment procedures, measures, and intervention content.

During a 4-year main outcome trial phase, the investigators will enroll 24 separate sociocentric ("bounded") social networks composed predominantly of Black MSM. Each sociocentric network will consist of the ring of friends surrounding an initial high-risk index as well as all friends surrounding persons in this second ring and then friends surrounding a successive third snowball ring of enrollees. Each 3-ring sociocentric network is expected to consist of approximately 40 unique members (n=24 networks, each with 40 members = approximately 960 individual participants).

All participants will be assessed at baseline to measure sexual practices, substance use, and other risk characteristics over the past 3 months; asked to provide biological specimens to be tested for HIV and other sexually transmitted diseases (STDs); and counseled in HIV/STD risk reduction. STDs will be treated and those with HIV will be referred for treatment.

The investigators will identify the individuals in intervention condition networks with the greatest number of reciprocal interconnections and the most favorable sociometric standing in the network. These individuals--expected to constitute approximately 20% of the sociocentric network and designated as network leaders--will be recruited to attend a 9-session program that provides training and guidance in how to deliver on-going, theoretically-based, and culturally tailored risk reduction advice and counseling to other members within the same network.

Six and 18 months following the intervention, all participants will be reassessed on risk behavior and STD/HIV laboratory measures as well as measures of intervention exposure, with positive STD and HIV cases respectively treated or referred to care at each assessment point. Outcome analyses will test whether there is greater reduction in high-risk sexual practices, substance use associated with risky sex, and HIV/STD incidence within social networks in the intervention condition. The primary trial endpoints are reductions in prevalence and frequency of unprotected anal intercourse with nonexclusive partners, increased condom use, and lower incidence on a composite biological measure of new HIV/STD disease during the followup period.

Inclusion Criteria:

• are age 18 or older;
• except for the initial index, were named as part of a friendship circle of an already-enrolled participant;
• provide written informed consent and do not exhibit intoxication, drug use,or psychiatric impairment that leads the research staff member to question capacity to provide informed consent;
• can complete study measures and participate in study activities in English;
• reside in or near the study city and do not have definite plans to leave the area in the next 12 months.

Exclusion Criteria:

• are age 17 or younger;
• exhibit intoxication, drug use, or psychiatric impairment such that they are unable to provide written informed consent;
• cannot complete study measures or adequately comprehend study activities conducted in English; or
• live in a location distant from the study city.