Of 32 unrelated children with serum IgE greater than 1,000 U/ml, 17 were found to have infection proneness according to standard clinical criteria, and 15 were not infection prone. There were no statistical differences between these 2 groups of children with regard to age, sex, serum IgE levels or prevalence of asthma. However, the prevalence of eczema was significantly lower in the infection-prone group (p = 0.035). Of greater interest was the finding that 7 children in the infection-prone group had IgG subclass and/or IgA deficiency compared with none in the non-infection-prone group (p = 0.006). These results suggest that IgG subclass studies may be warranted in children with markedly elevated levels of serum IgE and proneness to infection.