It is known that irradiated individuals show persistent chromosomal damages and are at greater risk of developing leukemia. In the case reported here, chronic myelogenous leukemia was diagnosed in a man three years after irradiation for surgically removed bronchogenic carcinoma. The Philadelphia chromosome was found in blood metaphases. Chromosome alterations were present in four parallel cultures of a skin biopsy taken from the site of previous irradiation. All 122 karyotyped metaphases were abnormal although their mode was diploid or near diploid or in the range of 4n for the relatively frequent polyploid cells. In this material marker chromosomes permitted the sorting of cells within five stemlines. One of the marker chromosomes in skin metaphases had the features of the Philadelphia chromosome, showing satellites and acrocentric association, although it may have arisen from any of the ten satellite acrocentric chromosomes. As a rule, studies of X-ray induced damages to blood cells in non-leukemic man have not indicated clonal perpetuation of chromosome anomalies. This case suggests that clonal evolution may have been part of regenerative processes stemming from radiation-modified survivor cells in solid tissue.