Ki-ras activation by point mutation on codon 12 has been reported in non-small-cell lung carcinomas and in various models of experimental lung tumours induced by chemical carcinogens. The cellular targets for carcinogenic compounds of tobacco smoke are usually considered to be the cells of the bronchial mucosa or alveolar epithelium. However, little is known about preneoplastic events in bronchopulmonary carcinogenesis. The hypothesis of the presence of widespread target cells containing Ki-ras mutation was investigated by evaluating concurrent neoplastic and non-neoplastic bronchial and alveolar samples from 51 patients with non-small-cell lung carcinomas. The polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method used can detect one cell with a mutation on codon 12 among 10(2) normal cells. In tumour samples, a mutation was detected in 20% of adenocarcinomas, but in none of the adenosquamous or squamous cell carcinomas. No mutation was detected in the non-neoplastic bronchial or parenchymal samples. When using an enriched PCR-RFLP method detecting one mutated allele among 10(3) normal alleles a mutation was detected in 23% of adenocarcinomas. In conclusion, Ki-ras activation by mutation on codon 12 was not observed in non-neoplastic bronchial or parenchymal tissues in patients with bronchopulmonary cancers and does not appear to be a genetic event present in non-malignant epithelial target cells exposed to tobacco smoke.