During two large outbreaks, ten episodes of histoplasmosis were documented in eight renal allograft recipients. Another episode occurred before the outbreaks. Associated infections with cytomegalovirus occurred in five patients and may have further impaired cellular immunity. Prolonged fever was the predominant clinical finding; and dissemination was observed in seven of our nine patients, including three with meningitis. Special stains of tissues and the histoplasmal complement fixation test provided useful diagnostic information rapidly, while cultures were eventually positive in seven patients. Treatment with amphotericin B resulted in prompt clinical improvement in all patients, but relapse occurred in two patients one year following therapy.