1. The carcinogenic activity of 20-methylcholanthrene for the forestomach of pedigreed mice has been confirmed.

  2. The periodic injection of MCA into the wall of the cecum produced focal mucosal hyperplasia in three animals (two injections, three injections, and four injections, respectively, in 20–44 weeks).

  3. One animal, sacrificed at 23 weeks after two injections of MCA into the wall of the cecum, developed a localized carcinoma of the cecum, the first adenocarcinoma to be reported after exposure of this organ to MCA.

  4. The repeated introduction of MCA into the sigmoid in the form of pellets did not result in carcinoma of the sigmoid or rectum.

  5. 20-Methylcholanthrene is less effective as a carcinogenic agent in the colon than it is in the stomach of the mouse, at the concentration used.

*

This investigation was supported by Grant No. C-1571 (C), U.S. Public Health Service, National Institutes of Health, Bethesda 14, Maryland.

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