BACKGROUND: Tumor growth is the net result of intrinsic proliferation and escape from active cell death. bcl-2 is a member of a new category of oncogenes that is not involved in influencing cell proliferation but is involved in regulating cell death(apoptosis). Based on this information, it seems to be reasonable to expect that there may be clinical prognostic significance of bcl-2 expression in non-small cell lung cancer. But its prognostic significance is not established. METHODS: To investigate the role of bcl-2 in lung cancer, we performed immunohistochemical stain of bcl-2 on 57 biopsy specimens from resected primary non-small cell lung cancer. Thereafter, flow cytometric cell cycle analysis was done. And we analyzed the correlation between bcl-2 expression, clinical parameters, S-, G1-phase fraction and survival. RESULTS: 1) bcl-2 were detected in 43.8% of total 57 patients(according to histology, squamous cancer 47%, adenocarcinoma 32%, according to TNM stage, I 28.6%, II 52.3%, III 45.5%. both differences were insignificant). 2) By using the flow cytometric analysis, mean S-phase fraction of bcl-2(+) and (-) group were 14.1(+/-7.8)%, 24.7(+/-10.5)%(p<0.005), mean G1 -phase fraction of bcl-2(+) and bcl-2(-) group were 75.5(+/-10.8)%, 65.5(+/-11.4)%(p<0.05). 3) 2yr, 3yr and 5yr survival and median survival time of bcl-2(+) group were 65%, 54%, 41%, 53months, and those of bcl-2(-) group were 71%, 52%, 46%, 37 months. (p>0.05, Kaplan-Meier, log rank) CONCLUSION: bcl-2 was detected in 43.8% of primary non-small cell lung cancer. The S-phase fraction of bcl-2(+) group was less than bcl-2(-) group, and G1 -phase fraction of bcl-2(+) group was more than bcl-2(-) group. But, expression of bcl-2 could not be a prognostic factor.