Rat skin carcinogenesis by topical applications of some azo dyes.

Groups of 6 male rats were painted twice weekly with 1 ml of a 0.2% solution of an azo dye in acetone. The dyes used were aminoazobenzene, 4-monomethylaminoazobenzene, their 3methoxy analogs, and 4-dimethylaminoazobenzene. In each case, all rats developed multiple skin tumors of histologie types similar to those found in rats treated with other chemical classes of carcinogen. 3-Methoxy-4-monomethylaminoazobenzene was the most potent carcinogen, followed by 4-monomethylamino azobenzene, 3-methoxyaminoazobenzene, and 4-dimethylamino azobenzene, and finally aminoazobenzene. 3-Methoxy-4-dimethylaminoazobenzene, which is also a potent carcinogen for rat skin, was found to be totally ineffectual when painted on the skins of 280 mice.