Molecular screening may increase the likelihood to identify early malignant lesions in non-small cell lung cancer. However the presence of gene mutations in non-malignant bronchial tissue has remained controversial. The present study was carried out to investigate systematically the presence of mutations of the K-ras and p53 gene in bronchial biopsies taken during routine bronchoscopy of normal as well as tumour tissues from a series of 40 patients with histologically verified non-small cell lung cancer (NSCLC). K-ras mutations were analysed with specific detection oligonucleotides, p53 mutations were examined by SSCP analysis. In all biopsies the wildtype of both K-ras and p53 could be detected. The overall frequency of mutations was 14 (35%) with 2 K-ras mutations (5%) and 12 mutations of the p53 gene (30%). In 3 cases (1 ras mutation, 2 p53 mutations) the same mutation could be shown in the tumour biopsy and in the distant normal control. In another case only the normal appearing tissue had a mutation of the p53 gene. All other mutations could be detected in the tumour tissue only. Our data confirm that K-ras mutations and p53 can be detected not only in malignant but also in non-malignant bioptic samples from patients with NSCLC. The use of molecular screening for the early detection of lung cancer may be a promising new approach.