A prospective study was initiated in 1979 to investigate the effect of hexamethylmelamine (HMM) as a second-line chemotherapeutic agent in the treatment of advanced adenocarcinoma of the ovary after failure of cisplatin-based multiple-agent chemotherapy. Of 20 evaluable patients, there were 5 patients (25%) who had objective responses (4 complete and 1 partial). Four additional patients have remained without evidence of disease. Six of these 9 patients are still alive, disease free. There were significant differences (P less than 0.001) in both the progression-free interval and survival time for these 9 patients, 13.3 and 15.1 months, respectively, as compared to the 15 nonresponders, 0.8 and 5.8 months, respectively. There was no significant difference in survival between the 4 patients with stable disease and the 11 patients with progressive disease. Performance status less than 2 (P less than 0.05) and absence of clinically measurable disease at the time of entry into the study (P less than 0.05) were found to be significant variables with regard to determining outcome. Only 2 of 24 patients suffered severe enough side effects from the HMM to warrant its discontinuation. This study demonstrates that HMM at doses of 6-8 mg/kg/day for 21 out of every 28 days can induce a complete response and provide an extended disease-free interval and prolonged survival with tolerable side effects in a significant number of patients with ovarian cancer who have previously failed cisplatin-based multiple-agent chemotherapy.