A phase II trial of ifosfamide (isophosphamide, NSC 109724) and mesna (2-mercaptoethane sodium sulfonate, NSC 113891) in women with advanced or recurrent mixed mullerian tumors of the uterus was conducted by the Gynecologic Oncology Group. The starting dose of ifosfamide was 1.5 gm/m2 daily, intravenously, for 5 days. The starting dose of ifosfamide was reduced 1.2 gm/m2 daily in patients who had received prior radiotherapy. Mesna was given intravenously immediately and at 4 and 8 hours after the administration of ifosfamide. Each mesna dose was 20% of the total daily dose of ifosfamide. Twenty-nine patients are evaluable for toxicity, and 28 patients are evaluable for response. Twenty-one patients had received prior abdominal hysterectomy, and eight patients had prior radiotherapy. Thirteen tumors were homologous and 15 heterologous. Gynecologic Oncology Group grade 3 or 4 granulocytopenia occurred in seven (25%) patients and two (7.1%) had grade 3 or 4 thrombocytopenia. Two patients (7.1%) had grade 3 or 4 neurotoxicity. One patient experienced lethargy and confusion that responded to discontinuation of the ifosfamide. A second patient developed progressive cerebellar dysfunction, left hemiparesis, and coma. This patient died after 3 days of therapy. Complete responses were seen in five (17.9%) patients and partial responses occurred in four (14.3%) patients for a total response rate of 32.2%. These results indicate that ifosfamide is an unusually active drug in patients with advanced or recurrent mixed mullerian tumors of the uterus. Studies with combination regimens incorporating ifosfamide are warranted. The toxicity of ifosfamide in Gynecologic Oncology Group studies is being evaluated retrospectively.