Testing of some benzidine analogues for microsomal activation to bacterial mutagens.

Analogues of benzidine were assayed for mutagenic activity towards Salmonella typhimurium TA 1538 in the presence and absence of a liver enzyme preparation. Purified 3,3'-dichlorobenzidine and the technical grade material had some direct mutagenic activity, but this was increased over 50-fold by addition of a liver mixed function oxidase preparation. In the presence of the liver preparation, 3,3'-dichlorobenzidine was approximately 10 times more active than benzidine, while 3,3',5,5'-tetrafluorobenzidine was of approximately equipotency. On the other hand, 3,3',5,5'-tetramethylbenzidine had no mutagenic activity alone or in conjunction with a liver preparation. 3,3'-Dianisidine had slight mutagenic activity in the presence of liver but none in its absence.