Carcinogenic Activity of Analogues of p-Di- methylaminoazobenzene. V. Effect of Added Methyl Groups in the Pyridine Series 1. 2. 3

were compared for rat hepatocarcinogenic activity at 0.03, 0.02, and 0.01 % levels in the diet. Two other dimethyl derivatives were prepared where a methyl group is substituted in the benzene ring that carries the dimethylamino group. These were both found to be active, in contrast to the situation with p-dimethylaminoazobenzene (DAB) homologues. The N-methyl-N-ethyl, N,N-diethyl, and N,N-dipropyl homologues of N,N-dimethyl-4-(4'-[pyri-dyl-1 '-oxidelazo)aniline were prepared and tested. In contrast to the situation in the DAB series, the N,N-diethyl homologue was active.-J Nat Cancer Inst 37: 365-367,1966. IN THE SECOND paper of this series (1) we showed that N,N-dimethyl-4- ( 4 '- [2 '-methylpyri-dyl-l '-oxide]azo)aniline (2'MeP04) was the most active of a group of monomethyl-substituted pyridine azo compounds in producing hepatomas in rats. When an additional methyl group wa