In vitro Transformation of BALB/c 3T3 Cells by 1,1,2,2‐Tetrachloroethane

1,1,2,2‐Tetrachloroethane (1,1,2,2‐TTCE) was shown to be capable of inducing in vitro transformation of BALB/c 3T3 cells (clone A‐31) either in the presence or in the absence of S9 activating system using an amplification‐transformation (level‐II) assay by reseeding confluent cells from each treatment and allowing additional rounds of cell replication. In the absence of metabolic activation, the highest assayed dose (1000 μg/ml), exerting the highest toxicity, was the only transforming dose. Lower doses of 1,1,2,2‐TTCE were capable of transforming BALB/c cells in the presence of S9 activating system, the dose of 500 μg/ml exerting the highest transforming activity. The number and size of transformed foci recognized in the level‐II plates were a function of the number of cells reseeded in the amplification assay. Foci obtained in the presence of S9 activating systems were larger in size, more deeply basophilic, and exhibited denser multilayering of constituent cells than foci recognized in the absence of exogenous metabolic activation.