Morphologic alterations in epithelium, caused by imcompetency of retinoids in a diet, were similar to those, obtained after treatment with chemical carcinogens. This suggests to use various derivatives of nature retinoids for treatment of epithelial tumors in skin and other tissues. Cultures of mouse prostatic gland and skin epithelium from metatarsus of chicken embryo were used for study of antitumoral activity of various synthetic retinoids. The most active preparations proved to be cyclopentenyl- and trimethyl methoxyphenyl ethyl ester derivatives of retinolic acid. The antitumoral effect of retinolic acid and its derivatives appears to involve a tight binding of the preparations with specific protein and inhibition of ornithine decarboxylase in tumor. The enzyme is well known to be related to synthesis of DNA, RNA and protein.