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.

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

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