SummaryWc report a case of severe isolated leukopenia in a patient with advanced breast cancer treated with aminoglutcthimide. Our patient had received no radiation therapy or cytotoxic chemotherapy during the six months prior to admission. Examination of the bone marrow revealed no abnormal cell infiltration. The patient recovered spontaneously. Wc believe that the leukopenia of this patient was due to aminoglutcthimide.