In a phase I study of weekly administered cisplatin, we observed a major response in 8 of 9 patients with locally far advanced head and neck cancer. Therefore, a phase II study was initiated to explore the activity and tolerance of this weekly cisplatin regimen. 59 patients with locally advanced head and neck cancer were entered into this phase II study. Cisplatin was administered at a dose of 80 mg/m2 weekly for 6 cycles. Cisplatin was administered in hypertonic saline (3% NaCl) as a 3-h infusion with standard pre- and posthydration. 51 patients were evaluable for response and 55 for toxicity. Only 9 patients were able to complete the treatment with the planned dose intensity of 80 mg/m2/week. Complete disappearance of the tumour was observed in 8 patients and a partial response in 22 (response rate 59%; 51% of all eligible patients 95% CI limits 37-63%). Stable disease was observed in 12 patients, and the tumour progressed in 9 patients. 47 patients subsequently received high-dose radiotherapy, 1 radiotherapy and surgery and 4 patients second-line chemotherapy. The median progression-free survival and median overall survival for all patients were 32 weeks and 56 weeks, respectively. Haematological toxicity consisted of anaemia, leucocytopenia (grade 3 + 4 in 17 patients) and thrombocytopenia (grade 3 + 4 in 17 patients). Because of leuco- and/or thrombocytopenia, treatment was delayed in 30 patients while 13 were taken off the study because of delayed bone marrow recovery. Non-haematological toxicities were: ototoxicity grade 1 in 3 patients, grade 2 in 7 and grade 3 in 3 patients; nephrotoxicity grade 1 in 13 patients, grade 2 in 2 and grade 3 in 1 patient. Neurotoxicity grade 1 was observed in only 8 patients. Cisplatin, as a single agent, administered at high-dose intensity, has an antitumour activity comparable with that of combination regimens in locally advanced head and neck cancer. The pattern of toxicity is different: leuco- and thrombocytopenia jeopardize the dose intensity concept; for patients ototoxicity is the more relevant toxicity. Further studies with weekly cisplatin are of interest particularly with newer measures to reduce toxicity.