Two cases of malignant disease occurring during immunosuppressive therapy, one a leiomyosarcoma of bowel metastatic to the liver, the other, carcinoma in situ of the cervix uteri, are reported. The possible roles of immunosuppression and immunosuppressive therapy in the pathogenesis of these neoplasms are discussed. It is suggested that the incidence of neoplasms in immunologically suppressed patients is greatly increased and that further investigation into the relation of immunosuppression to cancer is urgently needed.