In order to assess the maximum tolerated dose of 5'-deoxy-5-fluorouridine (5dFUR) combined with a cisplatin (20 mg/m2 i.v.) and L-folinic acid (100 mg/m2 i.v.), 5-day schedule 19 consecutive chemotherapy-naive patients affected by advanced or recurrent carcinoma of the head and neck were entered in this phase I trial. Doses of 5dFUR were escalated from a starting level of 2,000 mg/m2/day up to 3,000 and 5,000 mg/m2/day. At the latter step the dose-limiting acute toxicities were stomatitis and diarrhea, which were of WHO grade 3-4 and occurred in 3 and 1 out of 4 evaluated patients, respectively. Other grade 3 acute toxicities were leukopenia, anemia, renal impairment, and neurologic symptoms, observed in 1 patient each. Furthermore, one possibly treatment-related death was registered among patients entered in the highest dose level. Eleven out of 19 patients (58%; 95% CI:34-80%) showed a complete (2 cases) or partial (9 cases) response to this treatment, regardless of the 5dFUR dosage employed. From our results we may define the maximum tolerated dose of 5dFUR to be associated with cisplatin and L-folin acid used in this trial as 3,000 mg/m2/day x 5 days. Assessment of the real activity of this combination chemotherapy deserves further studies.