A study was conducted on 751 healthy children from child health clinics, kindergartens and schools, and 80 normal adults to establish reference ranges for serum immunoglobulins (Ig) G, A and M concentrations in normal Chinese. Serum IgG, IgA and IgM concentrations were determined by nephelometry. Serum IgG and IgA were shown to have a significant rise during the preschool age as well as at puberty with a plateau phase in between. This biphasic maturation profile has not been reported in Caucasians and the reasons for the observed difference have yet to be elucidated. Serum IgM concentrations were shown to be higher in females than in males, reaching significance in most age groups beyond 4 years of age. The difference between the two sexes in Chinese was of similar magnitude as that reported for Blacks and Caucasians, that is, 30%. Our findings support the hypothesis that the human X chromosome may carry quantitative genes for IgM.