Paclitaxel is a new agent for advanced non-small cell lung cancer (NSCLC). Weekly doses may enhance antitumor activity while minimizing toxicity, but little is known about immune recovery. Paclitaxel (80 mg/m2) was administered to 10 patients with NSCLC, weekly during 3-week cycles. Natural killer (NK) activity, CD3-CD16+CD56+ NK cells, and differential counts were monitored. NK activity appeared in all patients after treatment with paclitaxel therapy NK activity showed a 27 +/- 9% decrease (mean +/- SE) on protocol day 8 and a 37 +/- 7% decrease on day 15 (p < 0.05) recovering to 89 +/- 5% of baseline on day 29. With weekly paclitaxel, a decrease in NK cell function persisted through the first cycle but then recovered. Weekly paclitaxel may be less immunosuppressive than agents such as cisplatin.