Immune responses provoked by human immunodeficiency virus (HIV) infection ultimately are insufficient to control the disease and do not include strong lymphocyte-proliferative responses to HIV antigens or antibodies to many viral epitopes. A randomized double-blind, placebo-controlled trial evaluated the immunogenicity of recombinant HIV envelope vaccine (rgpl60) in HIV-infected subjects with ⩾$400/mm^3$CD4 T cells. Controls received hepatitis B vaccine. Of subjects receiving rgpl60, 98% developed lymphocyte-proliferative responses to the immunogen, 33% to a different envelope protein, and 56% and 60% to p24 and p66, respectively. All doses of vaccine (20, 80, 320, 1280 /μg) induced new responses. New antibodies to epitopes on rgpl60 developed only in recipients of higher doses of rgpl60. CD4 T cell percentages declined less rapidly in recipients of rgpl60 than in controls. Vaccination of HIV-infected subjects with rgpl60 results in cellular and humoral immune responses to HIV that infection itself had not stimulated.