Autoantibodies specific to HLA class I antigens were detected in the sera of persons vaccinated with human immunodeficiency virus type 1-derived recombinant vaccines by using synthetic peptides representing the amino acid sequences recognized by an HLA class I/gp120 cross-reactive monoclonal antibody. Study subjects received recombinant vaccinia gp160 (vacc-env) alone, vacc-env followed by one dose of recombinant gp160 (rgp160, 640 micrograms), or four doses of rgp160 alone (640 or 80 micrograms). All sera from vacc-env/rgp160-vaccinated subjects contained HLA/gp120 cross-reactive antibodies, as did all sera from recipients of the rgp160 alone at 640 micrograms/dose. In contrast, none of the sera from subjects who received either the vacc-env alone or the 80 micrograms/dose rgp160 alone contained detectable HLA cross-reactive antibodies, and these same sera showed little or no envelope reactivity on Western blot. The results showed a striking correlation between immunogenicity and the induction of cross-reactive antibodies by the rgp160 vaccine.