Healthy, adult volunteers without identifiable high-risk behavior for HIV-1 infection are randomly assigned to receive three injections of either 200 mcg gp160 vaccine or a placebo. At each participating site, four volunteers receive vaccine and two volunteers receive placebo. Primary immunization and two booster immunizations at day 30 and day 180 are done in an outpatient setting. Volunteers are closely monitored for the first 2 weeks postimmunization (primary and boosters), and extensively followed for 2 years. Volunteers may be offered an additional booster of the same preparation at 12 months.