Sequential chemotherapy and radiotherapy offer considerable improvements in the care of patients with locally advanced non-small cell lung cancer (NSCLC) and squamous cell carcinoma of the head and neck (SCCHN). Improved survival for lung cancer and organ preservation in head and neck cancer have occurred with this approach, but local control remains a problem. Concurrent chemotherapy and radiotherapy can potentially improve both local control and control of micrometastases. We previously showed that concurrent carboplatin plus radiotherapy is a useful potential treatment for advanced NSCLC and SCCHN, producing good local control and acceptable toxicity. Paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) has recently demonstrated strong single-agent activity against both NSCLC and SCCHN. Paclitaxel has also shown favorable interactions with radiotherapy and with platinum compounds. We therefore added weekly paclitaxel at 45 mg/m2 given after premedication and before carboplatin (100 mg/m2) weekly during concurrent standard-dose radiotherapy. Twenty patients (seven with SCCHN and 13 with NSCLC) have been treated (38 and 73 weekly doses, respectively). Toxicities have been manageable with delay or dose reduction in five and eight patients, respectively, for SCCHN and NSCLC. Based on these toxicities paclitaxel dose has been reduced to 40 mg/m2/wk. Plasma pharmacokinetics have shown that concurrent carboplatin and radiotherapy do not alter the pharmacokinetic behavior of paclitaxel compared with single-agent data. Concurrent therapy with carboplatin, paclitaxel, and radiotherapy is feasible on this schedule. Further case accrual to assess efficacy is ongoing.