We conducted a phase I study to evaluate the activity and tolerability of concurrent docetaxel and cisplatinum radiosensitization with hyperfractionated irradiation, in patients with advanced non-small cell lung cancer (NSCLC) and squamous cell carcinoma of the head and neck (SCCHN). Nine patients (5 stage III(A) and 4 III(B)) with NSCLC, and 15 with SCCHN (10 stage III and 5 IV) were treated with a b.i.d. hyperfractionated (HF) radiotherapy schedule. The normalized total dose for alpha/beta ratio = 10 Gy was 69.6 Gy for NSCLC and 80.5 Gy for SCCHN patients. The standard dose of cisplatin (10 mg/m(2)) was given combined to docetaxel on a weekly basis. The docetaxel starting dose level was 10 mg/m(2)/week and was escalated by 3 mg/m(2) increments in cohorts of 8 patients (5 SCCHN and 3 NSCLC). DLT (grade 3 malaise) was observed in 4 out of 8 patients treated at the 16 mg/m(2)/week docetaxel dose level. The 13 mg/m(2)/week docetaxel dose level was defined as the MTD causing grade 3 mucositis in 4 out of 8 patients. In total 4 (17%) patients developed grade 3 neutropenia. G-CSF support was given in 1/8, 4/8, and 5/8 patients treated at the 10, 13 and 16 mg/m(2) docetaxel dose levels respectively. Fatigue was the most common adverse event (5/24: 21%) and was responsible for more than 1 week treatment delay in 4 out of 8 patients treated at the 16 mg/m(2)/week docetaxel dose level. Nine (3 NSCLC and 6 SCCHN patients: 37.5%) had treatment delay of 1 week, while 7 (3 NSCLC and 4 SCCHN: 29%) had delays of 2 weeks for combined chemoradiation sequelae. Acute hypersensitivity reactions occurred in 3 (12.5%) patients, and grade 3 mucositis in 2/8, 5/8 and 6/8 patients, treated at 10, 13 and 16 mg/m(2)/week docetaxel dose levels respectively. The overall response rate was 79% (CI = 63-96%) with 33% and 53% CRs for NSCLC and SCCHN patients respectively. There were 3 deaths among 9 NSCLC and 4 among 15 SCCHN patients. Local and/or distant disease recurrences were shown in 4 NSCLC and in 6 SCCHN patients; 5 NSCLC and 9 SCCHN patients are alive with no evidence of tumor progression at 8.5 months mean follow-up time. Radiosensitization with docetaxel and cisplatin given concurrently with HF (b.i.d.) radiotherapy on a weekly basis is a promising approach and the recommended dose for further phase II studies is 10 mg/m(2)/week for both drugs. The antitumor activity shown was significant in both types of tumors. The incorporation of docetaxel in chemoradiotherapy regimens for future treatment of squamous cell carcinoma of the lung and head and neck, merits evaluation in phase II and III trials.