We investigated the association between maternal antibodies to HIV-1 peptides in pregnant women and the acquisition of HIV-1 infection by their offspring. Pregnant HIV-1-infected Haitian women were tested for the presence of antibodies against peptides of 14-17 amino acid length from the V3 loop region of strains IIIb and MN. Antibody testing was performed in two separate laboratories by enzyme-linked immunosorbent assay (ELISA). Peptides from four regions of the V3 loop were synthesized in several different laboratories and the purity confirmed by high performance liquid chromatography (HPLC). The mothers of infants who acquired HIV-1 infections did not differ significantly from the mothers of uninfected infants in the prevalence or concentration of antibodies to any of the 15 peptides evaluated. Additional studies are indicated to determine if neutralizing antibodies or other immunologic parameters are associated with maternal-infant HIV-1 transmission.