Deleted in pancreatic carcinoma locus 4 influences tumorigenesis and tumor progression by various mechanisms, including apoptosis. The aim of this study is to determine whether deleted in pancreatic carcinoma locus 4 participates in apoptosis in lung cancer and clarify its relationship with clinical parameters of non-small cell lung cancer. Immunohistochemical results revealed that the positive rate of deleted in pancreatic carcinoma locus 4 in normal tracheal-bronchial epithelium (89.5%, 17/19) was much higher than that in tumor tissues (63.5%, 33/52) (P < .05) and closely correlated with lymph node metastasis (P < .001). These results were further confirmed by Western blot analysis. Furthermore, deleted in pancreatic carcinoma locus 4 overexpression was inversely associated with Bcl-2 immunostaining (P < .01), and the apoptosis index in deleted in pancreatic carcinoma locus 4-positive carcinomas (8.65 +/- 1.46) was much higher than that in deleted in pancreatic carcinoma locus 4-negative carcinomas (2.12 +/- 0.04) (P < .05). The results of deleted in pancreatic carcinoma locus 4 small interfering RNA in A549 cells also showed that deleted in pancreatic carcinoma locus 4 could inhibit cell proliferation, decrease Bcl-2 mRNA and protein expression, and increase Bax messenger RNA and protein expression. These findings indicated that Deleted in pancreatic carcinoma locus 4 might be an important biomarker for malignant transformation and be involved in inducing apoptosis by modulating Bcl-2/Bax balance.