This Phase I/II study investigated weekly docetaxel (Taxotere) with concurrent radiotherapy in 42 patients with untreated stage III non-small cell lung cancer (NSCLC). All patients were treated with chest irradiation: 2Gy administered 5 days/week for 5 weeks, to a total of 50Gy. Docetaxel (1-h infusion) was administered on days 1, 8, 22, and 29< or =2 h before radiation fractions 1, 6, 16, and 21 (i.e. every week excluding the third week of treatment). In the Phase I study (n=12), docetaxel was started at 20 mg/m2 per week (n=3) and escalated in 10 mg/m2 increments (30 mg/m2, n=3; 40 mg/m2, n=6). Dose-limiting toxicity (grade 3-4 esophagitis) occurred with docetaxel 40 mg/m2. The Phase II study (n=30), therefore, evaluated docetaxel 30 mg/m2 (considered recommended dose). All patients except one experienced asymptomatic grade 3-4 lymphopenia; four patients (9.5%) had grade 3-4 esophagitis. The overall response rate was 45.5%, with eight (24.2%) complete responses. The median time to progression at the recommended dose of 30 mg/m2 (n=33) was 12.0 months and the median survival time was 13.6 months. The 1-year survival rate was 60.6%. Five patients (one from Phase I and four from Phase II) were alive after >5 years. In conclusion, weekly docetaxel 30 mg/m2 plus radiotherapy is active and well tolerated in stage III NSCLC.