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 3-methoxy analogs, and 4-dimethylaminoazobenzene. In each case, all rats developed multiple skin tumors of histologic 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-monomethylaminoazobenzene, 3-methoxyaminoazobenzene, and 4-dimethylaminoazobenzene, 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.


This work was supported by the Birmingham Branch of the British Empire Cancer Campaign for Research.

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