the concurrent presence of infectious organisms within cutaneous lesions of Kaposi's sarcoma (KS) in persons with the acquired immunodeficiency syndrome (AIDS) has been demonstrated. We report the first patient with AIDS in whom both KS and Histoplasma capsulatum were documented within the same cutaneous lesion. Pathogenic organisms of other fungal, mycobacterial, and viral diseases in KS lesions in other patients seropositive for human immunodeficiency virus are reviewed. Possible explanations for the coexistence of a focus of infection within a lesion of KS are discussed. It may be that in some patients the infection acts as a stimulus to induce vascular proliferation and subsequent development of sarcoma. There is also support for the idea of organism seeding in vascular tissues in the course of dissemination of infection. It is important to rule out the presence of coexistent infections or more than one pathologic process in skin lesions in patients with AIDS.