In recent years some interest has arisen concerning the influence of a dietary deficiency of vitamin A in the production of tumors in rats. Fuzimaki and his associates (1, 2, 3) reported that prolonged feeding of rats with a diet deficient in vitamin A was followed by the development of carcinoma in the fore-stomach of five rats out of 49 animals tested. One of the five animals developed metastases in the lungs. Their recent communication (4) indicated that the hyperkeratosis or atypical epithelial proliferation in the fore-stomach of albino rats was not marked unless the animals were fed with a diet deficient in fat, as well as in vitamin A. The investigations of Erdmann and Haagen (5) also lead to the conclusion that lack of vitamin A in the diet is an important factor in carcinogenesis. Following special feeding they found a number of rats with spontaneous tumors. Of the 83 specially fed rats, 6 developed tumors. Four tumors originated from the mammary gland of female animals. Three of the tumors were adenocarcinomas, and one was an angioma. Two other tumors were papillomas of the stomach. They stated that the great increase over the control animals (7 per cent against less than 1 per cent) could only be accounted for by the kind of diet eaten (6). In her last paper (7) Erdmann stated that after being subjected to a diet over-rich in vitamin B and D, eight rats in three series of experiments developed malignant growths. In the first series, consisting of 80 rats, 3 adenocarcinomas of the mammary gland developed (5). In the second series, consisting of 100 rats, one papilloma of the stomach appeared.