Mutations in the ras family genes (K-ras mainly) represent a common event in lung tumorigenesis which is frequently associated with poor clinical outcome. In order to investigate whether K-ras mutations are detectable in cytological material obtained from patients with lung cancer, 37 cytological specimens (16 fine needle aspiration and 21 bronchoscopy) were assessed for codon 12 point mutations in the H-, K- and N-ras genes by combined polymerase chain reaction-restriction fragment length polymorphism. K-ras codon 12 point mutations were found in 8 out of 37 (22%) specimens while no mutations were found in the H-ras and N-ras genes. Mutations were found in 27% (3 out of 11) of adenocarcinomas while in squamous cell carcinomas the incidence of mutations was 18% (3 out of 17). In addition, a K-ras codon 12 point mutation was found in one (12%) among 8 small cell carcinomas and in the only Hodgkin's lymphoma with metastasis in the lung. Our results are in agreement with previous results that recognise high incidence of K-ras activation in lung carcinomas, and indicate that detection of mutant ras alleles is possible in cytological material.