Eighteen infants of mothers with human immunodeficiency virus (HIV) infection were given hepatitis B vaccine at birth. Seroconversion occurred in all 13 infants whose HIV antibody disappeared, versus one of five HIV-infected children. The four of five HIV-infected infants who did not mount an antibody response progressed rapidly to full-blown acquired immunodeficiency syndrome. Thus HIV-infected infants respond poorly to hepatitis B vaccine.