In 159 healthy German children aged 3 months to 16 years IgG subclass concentrations were measured by radial immunodiffusion using polyclonal antisera. IgG-4 levels were also determined by a monoclonal ELISA kit (Binding Site). Both methods for IgG-4 determination showed a significant correlation (r = 0.91); the WHO reference serum 67/97 was used for calibration. The mean range and percentiles for age are given. IgG subclass levels were correlated with the age of the children in the order IgG-2 greater than IgG-1 greater than IgG-4, but this was not the case for IgG-3. The normal ranges of IgG subclasses were in good agreement with those of previous studies. No IgG-4 was detected by RID in only 8.8% of all the children, but in all aged 7 years and above.