Cell transformation represents a number of phenotypic changes observed in carcinogen-treated cells, including morphological alterations, anchorage independence and the acquisition of tumorigenicity on inoculation into suitable rodent hosts. Several cell culture transformation systems have been reviewed and reported to represent valid models for in vivo carcinogenesis . The BAIB/3T3 transformation assay was designed to allow the expression of transformed foci of high cell density and aberrant cell morphology an a confluent monolayer of nontransformed, contact-inhibited 3T3 cells. This system bas been demonstrated to be sensitive to the transforming activity of a variety of carcinogens. The BAIB/3T3 Clone A31-1 cell line was derived by Dr. T. Yakunaga, National Cancer Institute, Bethesda, MD from the aneuploid, nontumorigenic BAIB/3T3 Clone A31 cell line . This subclone is characterized by post-influence inhibition of proliferation and the ability to form distinct quantifiable foci of aberrant cell morphology following exposure to chemical carcinogens. The purpose of this study is to assess the morphological transforming potential of a series of structurally related test articles using the BAIB/3T3 done A31-1 mouse embryo cells in the absence of an exogenous metabolic activation system.