Nine chemicals classified as presumptive carcinogens on the basis of chronic rodent bioassays and one suspected human carcinogen which are reportedly not mutagenic to Salmonella typhimurium tester strains were tested for the ability to produce morphological transformation in Syrian hamster embryo cells in the absence of any exogenous source of metabolic activation. Acetamide, benzene, carbon tetrachloride, L-ethionine, monuron, piperonyl butoxide and trichloroethylene all induced positive morphological transformation in the presence of at least one of two medium and serum combinations as did the positive controls, ethyl methanesulfonate and benzo[a]pyrene. The remaining three chemicals, griseofulvin, isoniazid and trypan blue, did not induce morphological transformation under these same test conditions suggesting that they differ from the other seven chemicals in mechanism of action, target specificity or species susceptibility. Our results for seven of those ten selected chemicals in the clonal transformation assay using Syrian hamster embryo cells differ from their reported activity in the S. typhimurium point mutation assay. On the basis of this small sample, the Syrian hamster embryo transformation assay was a better predictor of the reported rodent bioassay results.