On the basis of results of testing of 212 peripheral blood samples from ethnic Chinese individuals in five age groups, ranging from birth to adulthood, by standardized flow cytometry techniques, we studied the maturational processes that are pertinent to monitoring the human immunodeficiency virus (HIV)-infected Chinese pediatric population. While the numbers of peripheral total white cells and percent lymphocytes declined from birth to adulthood, the percent CD3⁺ T lymphocytes was steady among all age groups studied. The numbers of CD3⁺ CD4⁺ (T-helper) cells decreased markedly after the first year of life, followed by a slower decline afterward and then a slight increase before adulthood. The trend for CD3⁺ CD8⁺ (T-suppressor) cells, however, was an increase among individuals of all age ranges. The numbers of CD19⁺ CD3 (B cells) increased only during the first year of life and then declined steadily, while natural killer (NK) cells showed the opposite pattern. Comparison of the results with those of studies done with a Caucasian population showed that both peripheral T-helper and T-suppressor cell numbers were low after the first year of life in the Chinese pediatric population in comparison with those in a Caucasian pediatric population. Lower B-cell counts and higher NK-cell counts were seen after the first year of life in the Chinese population than in the Caucasian population. It is important that for each HIV-infected population normative ranges of the lymphocyte subset be established to monitor HIV-infected pediatric patients.