Cytogenetic analysis of a squamous cell lung carcinoma revealed a near-haploid karyotype with 27 chromosomes, in both primary cultures and an established cell line. The only chromosomes with two homologs present were chromosomes X, 5, 7, and 22. The two X chromosomes were early and late replicating, respectively. No structural rearrangements could be detected. In vitro, the clone evolved by duplication towards hyperdiploidy with 54 chromosomes.