Mutations of the TP53 tumour suppressor gene have been reported for many human cancers. A variety of TP53 mutations have also been reported for both primary non-small cell lung cancer (NSCLC) and associated metastases. To assess the pathogenetic significance of TP53 gene alterations in NSCLC, 24 paired samples of primary NSCLC and the corresponding normal lung tissue were analysed for mutations of the TP53 gene (exons 5-8) using exon-specific PCR, single-strand conformation polymorphism PCR (SSCP-PCR) and direct DNA sequencing; for p53 protein accumulation by immunohistochemistry and for 17p allelic loss using restriction fragment length polymorphism (RFLP) probes on Southern blots and amplified fragment length polymorphism-PCR. TP53 point mutations were observed in 9/24 (38%) tumours encompassing a total of 14 mutations. Two tumours displayed the same double mutation while a third harboured four different mutations. Seventeen of 24 NSCLCs (71%) overexpressed p53 protein and all 17 immunopositive tumours (100%) showed a mutation and/or allelic loss at the D17S30 locus. Of the 17 NSCLCs informative at the DS17S30 locus, 10 (59%) showed allelic loss, of which five (50%) were also mutated on the remaining TP53 allele. These results suggest that TP53 gene alterations are involved in the pathogenesis of primary NSCLC and that such alterations may serve a selective role in the development of NSCLC by diminishing the apoptotic potential of bronchial epithelial cells heterozygous for a TP53 point mutation. This may also explain the accumulation of multiple TP53 point mutations in 3/24 of our NSCLC samples.