Five patients with disseminated histoplasmosis are reviewed. Four of five had the acquired immune deficiency syndrome (AIDS) and one was receiving steroid therapy. All were immigrants to the United States from Puerto Rico, the Dominican Republic, or South America, and none had a history of travel to regions of the United States where Histoplasma is endemic. Histoplasma complement fixation titers to mycelial antigen were not demonstrable in three of three patients in whom they were measured. Of the four patients with AIDS, Histoplasma capsulatum was isolated from bone marrow aspirates in two patients and from lymph node and liver biopsy specimens in one patient each. One of the bone marrow specimens showed organisms on Gomori-methenamine silver stain. In the other three cases, results of staining were falsely negative and diagnosis awaited culture results weeks later. Amphotericin B therapy resulted in rapid clinical improvement in the three patients that were treated. Intravenous therapy was followed by treatment with oral ketoconazole. Follow-up has not been long enough to determine the ultimate efficacy of ketoconazole. Disseminated histoplasmosis should be considered in all patients from the Caribbean or South America with AIDS or who are receiving immunosuppressive therapy.