The development of human adenocarcinoma of the lung involves multiple genetic changes including activation of oncogenes and loss of tumor suppressor genes. Patients whose lung tumors contain K-ras oncogene mutation, accumulation of the protein product of the tumor suppressor gene p53, or erbB-2/neu oncoprotein overexpression have been shown to have a worse prognosis. We examined these three genetic indicators in 29 lung adenocarcinomas to determine whether these markers are present in the same tumors or if they represent molecular changes that define different subsets of patients. P53 nuclear protein accumulation and erbB-2/neu protein overexpression were determined by immunohistochemical analysis of cryostat sections of tumor specimens and corresponding normal lung tissue. K-ras mutations were detected by radiolabeled oligonucleotide probes, specific for the various twelfth codon mutations, hybridized to exon 1 of K-ras, which was amplified by the polymerase chain reaction. Increased nuclear accumulation of p53 protein was found in 11 adenocarcinomas (38%). All of the p53 positive tumors were found to show high level staining and homogeneous expression of erbB-2/neu protein. K-ras mutations were detected in seven tumors (24%), all of which overexpressed erbB-2/neu. The presence of a K-ras mutation did not correlate with p53 accumulation. In total, 93% of the tumors were found to overexpress erbB-2/neu, the highest being in one tumor with erbB-2/neu gene amplification. The presence of K-ras twelfth codon mutation was associated with increased cigarette smoking. In conclusion, erbB-2/neu overexpression is a common event in lung adenocarcinomas. Furthermore, the presence of K-ras mutation and p53 protein accumulation define separate groups of patients. The mechanisms by which these genetic alterations interact or adversely affect prognosis is unknown.