Amonafide, a benzisoquinoline-1,3-dione was administered to 38 patients with recurrent or metastatic, bidimensionally measurable endometrial cancer. There were 34 patients with no prior cytotoxic chemotherapy, performance status of 0-2, and normal bone marrow, renal, and hepatic function were eligible for response and toxicity evaluation. Amonafide, 300 mg/ml, was administered intravenously over 1 hour daily for 5 consecutive days. Courses were repeated every 21 days. The major grade 3 or 4 toxicities were hematologic with granulocytopenia in 18 patients (53%), thrombocytopenia in 6 patients (18%), and anemia in 8 patients (24%). Infectious complications occurred in 3 patients (9%). Other side effects included cardiac dysrhythmias, hypotension, pain and phlebitis at the site of injection, nausea, vomiting, and flu-like symptoms. The overall objective response rate was 6% (95% confidence interval of 1-20%); 2 patients had a complete response (6%), 9 patients had stable disease (26%) and 21 patients had progressive disease (62%). Two patients had insufficient follow-up for response determination and are assumed to be nonresponders. The median survival of the eligible patients was 8 months. With the toxicity observed and the low response rate, amonafide at this dose and schedule has no efficacy in the treatment of endometrial cancer.