Sixty-four young adult male and female golden hamsters (Mesocricetus auratus) were divided into four equal experimental groups of sixteen animals. In Group 1 animals the left buccal pouch was painted three times weekly with a 0.25 percent solution of 7, 12-dimethylbenz(a)anthracene (DMBA) in heavy mineral oil. In Group 2 animals the left buccal pouch was similarly painted with DMBA, but the animals also received 7 I.U. of vitamin E (alpha tocopherol) twice weekly on days alternate to the DMBA painting. The vitamin E was administered orally via a fine pipette. Group 3 animals were similarly painted with DMBA and received vitamin E vehicle by pipette. Group 4 animals served as untreated controls. Four animals in each group (two male, two female) were killed at 8, 10, 12, and 14 weeks. Buccal pouches were photographed and excised. Tumors were noted and measured in the left buccal pouches. The buccal pouches as well as major organs were fixed in formalin, sectioned in paraffin, and stained with hematoxylin and eosin. In the Group 2 animals receiving vitamin E, there was a significant delay in tumor formation so that by 12 to 14 weeks there were fewer tumors and their average size was smaller than those in the Group 1 and Group 3 animals painted with DMBA but receiving no vitamin E supplement. Microscopic examination revealed that there was less invasion of underlying tissues and less surface necrosis. The tumors in both control and vitamin E groups were well-differentiated epidermoid carcinomas. No differences in the nature of the cellular patterns of the carcinomas in control and vitamin E groups were revealed by electron microscopic studies.