A male patient with hyperimmunoglobulin E syndrome is described. Recurrent lymphadenitis and cutaneous staphylococcal abscesses were resistant to various antibiotics, and chemotaxis and hydrogen peroxide production of polymorphonuclear leukocytes were impaired. Following trimethoprim‐sulfamethoxazole therapy, he was free from the above infections, and impaired polymorphonuclear leukocyte functions recovered and serum IgE decreased to approximately one‐fifth of its initial level. Subsequent irregular medications, however, resulted in impairment of polymorphonuclear leukocyte functions and an increased serum IgE concentration, which recovered after regular resumption of trimethoprim‐sulfamethoxazole treatment. From these results, the beneficial effects of trimethoprim‐sulfomethoxazole in hyperimmunoglobulin E syndromgak clinically apparent, but in vitro studies failed to demonstrate the positive effect of trkethoprim‐sulfamethoxazole on polymorphonuclear leukocytes and their mechanism still remains to be e