From a cohort of 162 children born to 161 mothers belonging to risk groups for human immunodeficiency virus (HIV) infection, we have studied 32 asymptomatic HIV seropositive and 19 HIV seronegative mothers and their offspring seropositive mothers when compared with the seronegative group had lower counts of leukocytes, lymphocytes, CD4+ cells and CD4+/CD8+ ratio as well as higher IgG and IgM serum levels. The offspring from HIV seropositive mothers differed from children born to HIV seronegative mothers in having higher lymphocyte counts, serum IgG level and spontaneous in vitro IgG production. The number of lymphocytes and the IgG serum level correlated in the child HIV seropositive mother pairs. Two children born to HIV seropositive mothers had a CD4+/CD8+ ratio below 0.8. The significance of these abnormalities and its possible relationship with active HIV infection in children is at present unknown.