BACKGROUND: Lung cancer is the leading cause of cancer over the world. P53 alteration is by far the most common genetic defect in lung cancer. The mutation of p53 protein involves the loss of inhibitory function of p53 related tumor suppressor gene and resultant oncogenesis. The analysis of p53 alterations consists of immunohistochemical stain, PCR based assay, or serologic ELISA (enzyme-linked immunosorbent assay). METHODS: Serum levels of p53 mutant protein were measured in 69 cases of lung cancer (adenocarcinoma n=29, epidermoid n=16, small cell n=13, large cell n=1, undifferentiated n=1, undetermined n=9) and 42 controls of respiratory disorders using ELISA. Immunohistochemical stain in tissue was performed using monoclonal antibody of p53 in lung cancer subjects. RESULTS: Both serum p53s in nonsmall cell cancer (0.28+/-0.44ng/ml) and in small cell cancer (0.20+/-0.14ng/ml) were not different from controls (0.34+/-0.20ng/ml). Also there was no significant difference in serum p53 according to tumor stages. P53 immunohistochemical stain showed 50% positivity overall in lung cancer. There were no close correlation between serologic level and positivity of immunohistochemical stain. CONCLUSION: The serologic determination of p53 mutant protein is thought to have no diagnostic role in lung cancer. Immunohistochemical stain in lung cancer specimen shows 50% positivity.