Abstract: Serum neuron-specific enolase（NSE） was determined in 29 patients with small cell lung cancer（SCLC） and the results were compared with those in 38 non-small cell lung cancer（NSCLC） and 35 non-carcinoma lung disease （NCLD）. The results showed that serum NSE level in SCLC group （27.3±14.5） was Significantly higher than that in NSCLC group （8.1±7.4） and that in NCLD group （5.5±4.4）, P＜0.01. Elevation of serum NSE was observer only in cases of stage Ⅲ or Ⅳ. Serial measurements performed on 15 patient’s With SCLC showed that serum NSE levels changed in parallel with clinical course during the treatment. The data suggests that serum NSE may be an available marker for monitoring disease extent and for determining response to chemotherapy in patients with SCLC.