Research on dominant oncogenes and tumor suppressor genes has characterized differences in genetic lesions between small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) and identified associations with clinical parameters. More than one half of all lung cancers contain a mutation of the p53 tumor suppressor gene. There does not appear to be an association between the presence of this mutation and survival. A ras family oncogene was found to be mutated in approximately 20 percent of tumors and tumor cell lines from patients with NSCLC in contrast to none of 45 tumors and tumor cell lines from patients with SCLC. The presence of a K-ras mutation was determined to be an adverse prognostic factor for survival in retrospective studies of patients with NSCLC. Mutations of K-ras are more common in tumors from smokers than nonsmokers and have not been detected in lung cancers resulting from occupational exposure to radon. Mutations in both the p53 gene and K-ras oncogene are most commonly G to T transversions in lung cancer vs G to A transitions in other cancers. Prospective studies of these mutations in resected tumor specimens taken from patients with accurate follow-up may continue to provide important clues about their potential clinical and biologic significance.