59 patients with histological verified squamous cell carcinoma of the head and neck, 39 with primary disease and 20 with relapse were given carboplatin and 5-fluorouracil (5-FU) in escalated carboplatin doses. The starting dose with carboplatin was 200 mg/m2 and the dose was escalated to 300 mg/m2, 350 mg/m2, 400 mg/m2 and thereafter by 20 mg/m2 per step. All patients received a dose of 1000 mg/m2 5-FU as a continuous infusion for 5 days. The myelotoxicity was moderate. No patients had grade 4 haemoglobin toxicity, while 7 patients had grade 3 toxicity. 2 patients had grade 4 leucocyte toxicity and 1 patient had grade 3. 4 patients were observed with a grade 4 platelet toxicity. 2 early deaths occurred at a dose level of 420 mg/m2. 18 out of 39 patients in primary treatment responded while 2 out of 20 patients treated for relapse responded. On the basis of the present study the maximum tolerable dose for carboplatin in combination with 5-FU 1000 mg/m2 is between 350 and 400 mg/m2.