On the basis of a Phase I reevaluation of thio-TEPA in which 3 of 9 patients with ovarian carcinoma responded, we instituted a Phase II study at high doses. Fourteen patients with a histologic diagnosis of epithelial carcinoma of the ovary, who had received at least one prior cisplatin-based regimen, were entered. Thio-TEPA was initially administered intravenously at a dose of 65 mg/m2 every 4 weeks, but was reduced to 50 mg/m2 after severe myelotoxicity developed in the first 5 patients. In 4 patients stable disease lasted 3, 4, 5, and 9 months; 10 patients progressed. There were no objective responses. At this dose and schedule, thio-TEPA has a response rate less than 20% in ovarian cancer patients previously treated with cisplatin.