The cytotoxic effects of gemcitabine (G) and cisplatin (C) seem to occur through induction of apoptosis. To examine whether the efficacy of GC chemotherapy might be influenced by the expression of death receptor 5 (DR5) and Bcl-2 of the tumor, we investigated the correlation between the tumor response rate and DR5 and Bcl-2 expression in a series of patients prospectively treated with GC. Thirty-four chemotherapy naïve patients with advanced non-small-cell lung cancer (NSCLC) received intravenously 1000 mg/m2 gemcitabine on d 1 and 8 along with 80 mg/m2 cisplatin on d 2, every 21 d. Tumor specimens were analyzed for DR5 and Bcl-2 expression by immunohistochemistry. The objective response rate was 56% (19 of 34 patients). With median follow-up of 10 mo, the predicted median survival time was 12 mo (95% confidence interval [CI], 9-15 mo). Eleven (32%) and 14 (41%) NSCLC cases were found positive for DR5 and Bcl-2, respectively. The response rate was significantly higher in patients with DR5 expression than those without DR5 expression (91% vs 39%; p = 0.008). Patients with Bcl-2 expression were apparently less responsive than those without Bcl-2 expression (21% vs 80%; p = 0.001). DR5 and Bcl-2 expression was significantly associated with response to GC chemotherapy. Therefore, DR5 and Bcl-2 status are useful factors for predicting the efficacy of GC.