Gemcitabine and paclitaxel are among the most active new agents in non-small cell lung cancer (NSCLC) and are worth considering for second-line chemotherapy. In this phase I-II study, we combined gemcitabine and paclitaxel for second-line treatment of advanced NSCLC. Gemcitabine doses were kept fixed at 1000 mg/m2 on day 1 and 8, and paclitaxel doses were escalated from 90 mg/m2 on day 1 of the 21-day cycle. Thirty-seven patients were treated at six different dose levels. Grade 4 neutropenia was dose-limiting toxicity (DLT), since it occurred in two out of six patients treated at paclitaxel 240 mg/m2; the paclitaxel dose level just below (210 mg/m2) was selected for phase Il evaluation. Non-hematologic toxicity was mild. One complete response (CR) (3%) and 13 partial responses (PR) (36%) were observed in 36 evaluable patients for an overall response rate of 39% (95% C.I., 23-57%). Median duration of response was 35 weeks (range, 8-102). All of the observed objective responses occurred in the 19 patients who had previously responded to the first-line therapy. Median survival was 40 weeks (range, 8-108 weeks). The combination of gemcitabine and paclitaxel is a feasible, well-tolerated, and active scheme for second-line treatment of advanced NSCLC; further evaluation, at least in selected patients, such as those previously responding to first-line chemotherapy, is definitely warranted.