Because vertical transmission of human immunodeficiency virus type 1 (HIV-1) from mother to infant occurs in only 15%-35% of possible opportunities, natural immune defenses of the mother, fetus, or neonate may be protective against infection. The relation between antibody-dependent cellular cytotoxicity (ADCC) antibodies and HIV-1 infection was explored in 78 neonates born to HIV-infected women. More than 90% of sera had measurable ADCC titers against HIV-1IIIB Infant titers were closely correlated with maternal titers but were independent of total IgG and total antibody reactive to the same strain in whole virus ELISA. At birth, mean ADCC antibody levels of infants or their mothers were the same for infants who were infected and those who ultimately seroreverted and remained healthy. ADCC antibody titers against HIV-1SF2 were weakly correlated with anti-HIV-1IIIB titers and did not predict protection from HIV-1 infection. High levels of anti-HIV-1 ADCC antibody at birth are not protective against vertical transmission of HI V-I.