A tumorigenic cell line (CHAUT) derived from a spontaneous uterine leiomyosarcoma of the Chinese hamster was established, and two clones (CHAUT-C and CHAUT-G) were characterized cytogenetically by both G- and C-band techniques. In both clones, all cells analyzed (53 in the C clone and 65 in the G clone) were distributed within a diploid range (24-26) with a modal number of 25. Their karyotypes were also characterized by four common changes; translocation of heterochromatic segment onto chromosome 2, tetrasomy of chromosome 10, monosomy of X chromosome, and one to three additional marker chromosomes of unknown origin.