Chronic granulomatous disease was diagnosed in a boy who suffered from severe generalized infections. Family investigations revealed the inheritance of the disease to be X-linked. However, unlike other cases of X-linked chronic granulomatous disease, the membrane oxidase of the neutrophils from this patient was not totally defective and sufficient activity was left to result in a normal phorbol myristate acetate-stimulated nitroblue tetrazolium slide test. Also, unlike the usual findings in X-linked chronic granulomatous disease, cytochrome b was present in normal amounts in the neutrophils from this patient. The cytochrome was normal, judged from its midpoint potential of -245 mV and its ability to bind CO. It is thus apparent that X-linked chronic granulomatous disease may result from at least two different defects and that the phorbol myristate acetate stimulated nitroblue tetrazolium slide test fails to detect some cases.