Chromosome findings in cultured skin fibroblasts from a patient treated with an anti-cancer drug, pepleomycin sulfate, for his penis cancer are reported. In two batches of specimens (days 16 and 34, respectively), out of 120 cells examined, a total of 26 abnormal cells (21.7%) were found with no common chromosome abnormalities; there were no clones. This cytogenetic pattern of abnormalities without clones in cultured skin fibroblasts differs from that seen in congenital disease or radiation-exposed skin fibroblasts. It is suggested that the anti-cancer agent is the most likely etiological factor for these uncloned chromosome abnormalities in cultured skin fibroblasts.