Progress in this research program is reported in the following six areas: Establishment of a cellular system in which somatic mutation, neoplastic transformation and differentiation can be investigated simultaneously - detection and characterization of subpopulations of contact-insensitive and anchorage independent cells in Syrian hamster embryo cell culture. Ploidy dependence of in vitro senescence. An alternate view of DNA sequence organization. Cell killing, somatic mutation and neoplastic transformation of SHE cells by DNase I encapsulated in liposomes - a normal procedure for a direct perturbation of a specific target in the genetic apparatus. Induction of heteroploidy in diploid human fibroblasts using antimitotic agents. Senescence and neoplastic transformation of Syrian hamster embryonic and adult fibroblasts.