Based on the demonstration of in vitro and in vivo synergy between cytosine arabinoside (Ara-C) and cis-diamminedichloroplatinum (CDDP), we designed a Phase II trial of Ara-C plus CDDP for patients with advanced squamous cancers of the head and neck and esophagus. Sixteen patients were treated on a unique schedule of continuous-infusion Ara-C, 30 mg/m2/day over 72 h, plus CDDP, 30 mg/m2/day at hours 12, 36, and 60 of the Ara-C infusion. The objective response rate was 38% (95% confidence limits 14-62%), with two patients achieving complete clinical and radiographic response (9 and 27+ months duration) and four partial responses (median duration 4 months, range 1-7 months). There was no CDDP-related nephro- or neurotoxicities, but a flu-like syndrome of anorexia and asthenia was common. Myelosuppression was the dose-limiting toxicity, necessitating Ara-C dose adjustments in 11 cycles of therapy and leading to fatal sepsis in one patient. We conclude that the activity of this combination, though comparable to that of other CDDP-containing regimens, offers no significant therapeutic advantage, and given the excessive hematologic toxicity, should not be investigated further.