Evaluation of previous patients who received doses of 40 or 80 mcg gp160 vaccine indicates that, although serum anti-gp160 antibody responses were detected, the level and duration of those responses were limited. A preliminary observation suggests that weak functional antibody responses may develop following the 18 month booster of 40 or 80 mcg; therefore, a dose of gp160 vaccine having potentially greater immunogenicity is of particular interest.