The development of Kaposi's sarcoma in immunosuppressed patients is a rare occurrence, but poses a real threat to the patient due to the rapid progression of the unchecked disease. The suspicion of this disease will prompt early diagnosis by scrutiny of histologic preparations and prompt interruption of antirejection therapy. Four of five patients in whom a diagnosis was made preterminally responded favorably to withdrawal of immunosuppressive agents. In renal allograft recipients with mucocutaneous vascular lesions, Kaposi's sarcoma should be considered as a cause of gastrointestinal bleeding.