T-lymphocyte subsets and serum immunoglobulins were assayed in 27 neonates and 12 infants younger than 6 months, all born to HIV-seropositive mothers. No differences in T-lymphocyte subsets between the 27 seropositive and 34 seronegative infants were found at birth. Twelve seroreverted and 14 infected children were followed. CD4+ cell counts were significantly lower in the latter at 3 and 24 months of age. Serum immunoglobulin levels and CD8+ percentages became higher in the infected group, starting from the sixth month, while CD4+ percentages and CD4+/CD8+ ratios became lower, starting from the twelfth month.