We study 37 children with mothers infected by human immunodeficiency virus type 1 (HIV-1) at birth and over the following three years. HIV-1 serology of these patients is reported, i.e., HIV-1 antigen p24 and antibodies using two commercially available enzymatic methods and Western blot. Throughout follow-up, IgG antibodies to HIV-1 showed a statistically significant tendency to decrease (p less than 0.001). After 12 months, 70% of the children lacked HIV-1 antibody banding by Western blot; this was taken to constitute a definitive criterion of lack of antibodies to HIV-1. Five children presented p24 antigenemia during the study, four persistently so. Of the patients over 18 months of age, 8 presented HIV-1 infection symptoms (30.7%), and three suffered AIDS (11.5%).