In order to establish normal reference ranges of serum immunoglobulin G subclasses for different age groups in Chinese, we measured the four IgG subclasses by radial immunodiffusion using polyclonal antisera in 350 normal healthy subjects (148 males and 202 females) recruited from the community. There was no significant sex difference for all the four IgG subclasses. Using Box-Cox transformation, we constructed smooth age-dependent percentile curves for the four IgG subclasses. For the 50th percentile values, the plateaus for IgG1 to IgG4 are respectively 970 mg/dl at 13 years old, 481 mg/dl at 18, 48 mg/dl at 17 and 80 mg/dl at 13. Methodology, reagents, environmental and genetic factors might be responsible for the observed difference among the various reports. The IgG2 level in our Chinese population seemed to be higher than that in Caucasians, which might account for the very low incidence of invasive Haemophilus influenzae type b disease among the Chinese. Our IgG1 level also plateaued later and at a higher level than that in other studies.