1. Rats were fed 0.064 per cent of m′ methyl-p-dimethylaminoazobenzene for 4 weeks, followed by 4 weeks during which certain dye-free diets were fed which altered the basal metabolic rate; the dye was then fed for another 4 weeks. Other rats were fed 0.06 per cent of p-dimethylaminoazobenzene (DAB) for 20 weeks in diets which altered the BMR.

  2. Hyperthyroid animals receiving DAB usually failed to survive, but the incidence of tumors in the survivors was high.Hyperthyroidism induced in precancerous rats in the absence of azo dye also increased tumor incidence. Thiouracil appeared to increase tumor incidence in rats fed DAB, but the more potent depressant, 6-n-propyl-2-thiouracil, failed to affect a development of tumors when given during the period of interruption.

  3. Liver slices from hyperthyroid rats destroyed less than one-fourth as much DAB as slices from normal rats. Slices from rats fed high levels of riboflavin destroyed nearly twice as much dye as slices from control rats, but when the rats which received high riboflavin were made hyperthyroid, the ability to destroy the dye decreased, although liver riboflavin remained high.

  4. In media containing inorganic salts and nicotinamide, homogenates from normal livers destroyed the dye at a high rate, while homogenates from hyperthyroid livers failed to destroy much dye. Homogenates from hyperthyroid livers destroyed approximately normal amounts of dye when hexose diphosphate was added to the medium.

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Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Supported in part by the Jonathan Bowman Cancer Fund and by a grant from the Committee on Growth, American Cancer Society.

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