To evaluate the contribution of hexamethylmelamine (HMM) to the treatment of advanced ovarian cancer with combination chemotherapy, we compared the results of treatment with HMM, cyclophosphamide, doxorubicin, and cisplatin (H-CAP regimen) to treatment results using cyclophosphamide, doxorubicin, and cisplatin (CAP regimen). The treatment regimens were identical in dosage and schedule with the exception of the addition of HMM to one regimen. Fifty-five patients treated with H-CAP at Vanderbilt University Hospital between August 1977 and March 1980 were compared with a subsequent group of 22 patients who received CAP between October 1984 and October 1987. Following six months of therapy, patients were restaged either with second-look laparotomy or with clinical restaging. Fifty-three of 55 patients (96%) had objective responses to H-CAP compared with 14 of 21 patients (67%) treated with CAP (p = 0.001). The pathologic complete response rate was also higher in the patients who received H-CAP (35% versus 19%). The median survival of patients receiving H-CAP is 47 months compared to 21 months for the CAP patients. When patients with limited residual disease (maximum tumor diameter less than or equal to 3 cm) were compared, the median survival also favored the H-CAP treatment (101 months versus 21 months, p = 0.002). The median time to progression was also greater in patients receiving H-CAP versus those receiving CAP (67 months versus 16 months, p = 0.045). Treatment-related toxicity did not differ substantially between the two regimens. Our findings suggest that the addition of HMM to CAP chemotherapy prolongs the median survival in patients with ovarian cancer and limited residual disease following cytoreductive surgery.