The combination of cisplatin 100 mg/m2 every 3 weeks and mitoguazone 500 mg/m2 every week with dose escalation was administered as a 9-week induction regimen to 27 patients with previously untreated Stage III or IV squamous cell carcinoma of the head and neck. This was followed by full-course radiation therapy for unresectable patients or surgery and postoperative radiation therapy for those with resectable disease. Sixteen patients had bulky unresectable disease, and ten were candidates for curative resection at study entry. Of 26 patients evaluable for response to chemotherapy, there were seven complete responses (CR) (five of six pathologically confirmed) and ten partial responses (PR) (65% CR + PR). Toxicity was generally mild with Grade 3 or 4 nausea and vomiting occurring in 15% and diarrhea in 12%. Nineteen percent of the patients developed transient nephrotoxicity (serum creatinine greater than 2), 62% anemia (hemoglobin decrease greater than 2 g/dl), 23% leukopenia (leukocyte count less than 3500 cells/microliters) and 8% thrombocytopenia (platelets less than 50,000 cells/microliters). Anorexia, fatigue, and weight loss occurred in nearly all patients. The median survival time of all patients was 17.5 months; complete responders, 43 months; partial responders, 16 months; and nonresponders, 9 months (P = 0.0025). In a multivariate analysis of stage, primary site, resectability status, response to chemotherapy, and local treatment (surgery plus radiation versus radiation), complete response was the only statistically significant covariate for survival. In Phase II single agent trials, mitoguazone has been shown to have a 15% response rate in head and neck cancer and cisplatin, a 30% to 40% response rate (less than 10% CR). Thus, our results, both complete and overall response rates, were higher than would be expected from either drug alone. A possible mechanism for this high response rate may be mitoguazone-induced cell synchronization. In vitro studies demonstrate the accumulation of tumor cells exposed to mitoguazone in S- and G2-phases of the cell cycle. These results would support further evaluation of mitoguazone in combination to explore the theoretical potentiation of antitumor effects by sequencing with cycle-specific agents.