Intercellular karyotypic compositions were studied in seven near-diploid cultured cell populations (including six cell lines) of human colorectal and fibrosarcoma origins. Within each population, 50-88% of cells had the same cell-line-specific karyotype. In five of these seven populations, coexisting minor cell types could readily be identified, implicating the frequent occurrence of mosaicism in transformed cell lines. Nearly 90% of these cell types showed a single chromosome loss or gain from the modal cell karyotype. Parameters that may assist in the evaluation of karyotypic diversity of a transformed cell line are discussed briefly.