Volunteers are randomized to one of seven groups to receive immunizations with either ALVAC-HIV vCP300 or ALVAC-RG vCP65 (control), plus simultaneous or sequential boosting with rgp120/HIV-1SF2 or placebo. Immunizations are given at 0, 1, 6, and 9 months or 0, 1, 3, and 6 months. Volunteers are followed for at least 24 months.