The amino acid sequence of HIV-1 gp120 can vary as much as 40 percent from isolate to isolate. Thus, the identification of an immunogen that can elicit broadly neutralizing antibodies to HIV-1 is a major challenge in AIDS vaccine development. Two candidate vaccines, recombinant envelope subunit proteins from the SF-2 and MN isolates of HIV-1, have shown immunogenicity and good tolerance in healthy immunocompetent adults. This study will expand testing into a larger population base, particularly targeting individuals at high risk for HIV infection.