A total of 5758 STD clinic patients were enrolled from 5 public STD clinics (Baltimore, Md; Denver, Colo; Long Beach, Calif; Newark, NJ; and San Francisco, Calif) between July 1993 and September 1996. Eligible participants were heterosexual, HIV-negative patients aged 14 years or older who came for full STD examinations. Using a block design, participating men and women were randomzied separately to 1 of 3 individual face-to-face interventions. Arm 1 received "enhanced counseling" consisting of 4 interactive counseling sessions based on the Theory of Reasoned Action and Health Belief Model. Arm 2 received "brief counseling", consisting of 2 interactive risk-reduction sessions based on CDC's client-centered counseling model. Arms 3 and 4 each received 2 brief didactic messages about HIV/STD prevention messages typical of current care at that time. Participants assigned to Arms 1, 2, and 3 were actively followed up after enrollment with questionnaires at 3, 6, 9, and 12 months and STD laboratory examinations and tests at 6 and 12 months. An intent-to-treat analysis was used to compare interventions. Arm 4 participants were followed passively to determine potential effects of active study follow-up.