We detected DNA aberrations at the RB locus in surgical specimens of human primary non-small cell lung carcinoma by single-strand conformation polymorphism analysis of polymerase chain reaction products amplified from regions of exons 2 to 27 including parts of the flanking intron sequences. Detection of nucleotide sequence polymorphism revealed loss of heterozygosity in six of eight informative cases among 13 squamous cell carcinomas analysed. In two of the six cases, mutations in the remaining allele were detected. In 25 adenocarcinomas analysed, no loss of heterozygosity was observed in 16 informative cases and a point mutation was detected in one of the uninformative cases. In one of three adenosquamous carcinomas analysed, a point mutation was detected and one adenoid cystic carcinoma analysed showed allelic loss of the RB gene. Our results indicated that loss of heterozygosity at the RB locus is frequent in squamous cell carcinomas of the lung, but not in adenocarcinomas. In the squamous cell carcinomas with allelic loss, mutations of the RB gene in the remaining alleles were found in one third of the tumors.