As part of a project within the European Community research activities on acquired immunodeficiency syndrome (AIDS), infants born to human-immunodeficiency-virus-seropositive mothers are being followed up from birth. By October, 1986, 71 infants from Padua, Berlin, and Edinburgh had been followed up to a median age of 6 months (range 1-15 months). Symptoms of AIDS or AIDS-related complex (ARC) had developed in 5, 3 of whom had died. The median age at antibody loss was during the 10th month. An estimated 75% will have lost maternal antibody by 12 months, but loss of antibody did not exclude infection confirmed by virus culture. Numbers were too small to draw conclusions about the risk of AIDS/ARC and mode of delivery or breast-feeding. The study suggested that the risk of AIDS/ARC is higher in infants born to mothers who have AIDS symptoms during pregnancy.