We have employed BALB/c 3T3 cells in a simultaneous cell transformation and mutation assay protocol to see whether both genotoxic and non-genotoxic carcinogens can be identified. Three known mutagenic animal carcinogens tested positive for transforming activity: dimethylnitrosamine, methylcholanthrene and methylnitrosourea. In addition, we tested three non-mutagenic compounds--two human carcinogens, benzene and diethylstilbestrol, and the possible human carcinogen dichlorodiphenyltrichloroethane; all three displayed transforming activity. These results add to existing data supporting the validity of the BALB/c 3T3 cell transformation system as a reliable short-term in vitro test for carcinogens in general, and for non-genotoxic carcinogens in particular.