The primary objective of the current study was to determine the maximum tolerated dose of paclitaxel (PTX) that could be added daily to radiation therapy (RT) in patients with non-small cell lung cancer (NSCLC). The secondary objective was to achieve a plasma concentration of PTX estimated to exert a radiosensitizing effect. Eighteen patients with locally advanced NSCLC were treated. 60 Gy of RT were given in 2 Gy fractions, 5 days per week. A daily dose of PTX was delivered by 4-h i.v. infusion before RT. The initial dose level of PTX was 9 mg/m2/day, escalated by 1 mg at each additional patient triplet. Two out of 6 patients experienced acute dose limiting toxicity (DLT) at the 12 mg/m2/day PTX dose level. PTX continuously greater than 10 nM, the estimated radiosensitizing condition, was achieved at the PTX dose level of 12 mg/m2/day. PTX at doses up to 11 mg/m2/day may be safely added to a conventional conformal RT course. Both DLT and the estimated radiosensitizing plasma exposure to PTX were encountered at the 12 mg/m(2)/day dose level.