A murine model was developed for assessing the effects of passively transferred polyclonal maternal anti-gp120 antibodies on the subsequent immunization of the offspring with recombinant gp120SF2 in complete Freund's adjuvant (rgp120SF2-CFA). Adult female BALB/c mice were immunized with rgp120SF2-CFA 6 weeks before mating. The 3-week-old offspring were subsequently immunized with the same vaccine and followed for 9 weeks. Both the total IgG anti-rgp120SF2 and the anti-V3 IgG antibody response to vaccine were inhibited in the experimental animals. The total IgG anti-rgp120SF2 response was < 20% of the control response (P < .001) 9 weeks after immunization. Anti-V3 antibody was also decreased. As vaccine studies begin in infants, the effects of preexisting antibody on the infant response to human immunodeficiency virus vaccines must be considered.