Hatched activated oncospheres of Taenia pisiformis penetrated the intestine and attained the liver within 40 min of their inoculation into the duodenum of the rabbit. Most oncospheres in histological sections were in the epithelium, but a few were noted in the lamina propria. It is suggested that oncospheres penetrate between epithelial cells and enter subepithelial capillaries without migrating extensively in the lamina propria. Secretions of the oncospheral glands may act as a lubricant. Penetrating oncospheres elicited no tissue reaction.