This is an open label study to determine the effects of the administration of Interferon-gamma on the clinical condition and immune function of patients with severe, treatment refractory non-tuberculosis mycobacterial infections. The study drug (interferon gamma) will be administered subcutaneously three times a week at 0.05 mg/m(2) for one year. We may also collect blood from the relatives of these patients and normal volunteers in order to characterize the genetic basis, if any, of our patients' disorders.