To determine whether IgG subclass concentrations differed between healthy black and white children, we measured IgG1, IgG2, IgG3, and IgG4 immunoglobulins by enzyme-linked immunosorbent assay in sera from 246 black children aged 6 to 42 months. We then compared these values with the normal values established for 664 white children aged 6 to 60 months. The IgG1, IgG2, and IgG4 subclass concentrations of the black children were lower than those for white children; many of the values were below the 95% confidence limits established for white children: 46 (19%) of 246 IgG2 values and 19 (8%) of 246 IgG4 values for black children were below the normal limits. We compared the geometric mean values for black and white children, as determined for each 6-month age grouping between 6 and 42 months of age; 367 of the 664 white children were less than 42 months of age and were included in this analysis. The geometric mean values for IgG1, IgG2, and IgG4 levels were consistently lower for black children than for white children. The differences were significant for IgG1 subclass values of those children older than 24 months and for IgG2 and IgG4 values of those children older than 18 months. No consistent differences were noted for IgG3 subclass values. We conclude that young black children have lower IgG1, IgG2, and IgG4 serum concentrations than are found in white children. If normal IgG values for white children are used, healthy black children may be erroneously classified as IgG subclass deficient. The mechanism and biologic relevance of these population differences need to be evaluated.