Non-small cell lung carcinoma specimens of 173 previously untreated patients were analyzed for the expression of proteins encoded by the oncogenes c-myc, c-fos, c-jun, c-erbB-1, c-erbB-2, c-H-ras, c-K-ras and c-N-ras. Forty-six per cent of the tumors were positive for the c-MYC protein, 60% for c-FOS, 50% for c-JUN, 80% for c-ERBB-1, 55% for c-ERBB-2, 12% for c-H-RAS, 5% for c-K-RAS and 71% for c-N-RAS. Proteins encoded by c-fos and c-jun are overexpressed more frequently in carcinomas of smokers (c-fos: P < 0.005; c-jun: P < 0.01). When we grouped the patients according to their tumor histology the results became more evident. Squamous cell lung carcinomas of smokers showed a higher incidence of c-FOS (P = 0.01), c-JUN (P < 0.01) and c-ERBB-1 (P = 0.01) proteins than squamous cell lung carcinomas of non-smokers. The expression rate and the intensity of staining proved not to be influenced either by the number of cigarettes smoked daily or by cessation of smoking. In adenocarcinomas, however, we only found a trend for a more frequent overexpression of c-fos (P = 0.07) and c-jun (P = 0.14) encoded proteins in carcinomas of smokers and no correlation between the expression of c-erbB-1 products and smoking. No correlation was found between the expression of c-MYC, c-ERBB-2, c-H-RAS, c-K-RAS and c-N-RAS proteins and the smoking habits of the patients, neither in squamous cell carcinomas nor in adenocarcinomas of the lung.