In this study, we evaluated the clinical usefulness of ProGRP and NSE for diagnosis and prognosis of small-cell lung cancer (SCLC). Serum levels of ProGRP and NSE were determined in 108 healthy subjects, 103 patients with benign pulmonary diseases, 142 with non-small cell lung cancer (NSCLC), and 114 with SCLC. Sensitivity of ProGRP in diagnosis of SCLC was significantly higher than that of NSE (64.9 vs. 43.0%, P < 0.001). The difference was substantial in patients with limited disease (56.5 vs. 20.3%, P < 0.001). However, 11 of 40 SCLC patients with normal levels of serum ProGRP (27.5%) showed elevated levels of serum NSE. In the SCLC patients receiving chemotherapy, the CR rate in patients with elevated NSE levels was significantly lower than in patients with normal levels of NSE (18.5 vs. 61.7%, P < 0.001). Elevation of both ProGRP and NSE was a poor prognostic factor, and patients with elevated levels of either ProGRP or NSE showed shorter survival than those without. From multivariate analysis, NSE was found to have a greater effect on survival of SCLC patients than ProGRP. These findings indicate that ProGRP is more sensitive than NSE for diagnosis of SCLC, while NSE is superior to ProGRP as a prognostic factor. In conclusion, both ProGRP and NSE are useful tumor markers and they have a complementary role for each other in diagnosis and prognosis of SCLC.