Our studies were focused at an early developmental stage of sexual differentiation in the ovine embryo. The development and differentiation of indifferent gonad into testicles was investigated. The comprehensive knowledge in this sphere is lacking and applies mainly to laboratory animals and man. The embryos of artificially inseminated ewes of the Slovak Merino breed were recovered by laparotomy on days 26, 28, 30, 35, 37, 40 and 45 of intrauterine development. The material was prepared for an examination by light and transmission electron microscopy. The morphological picture of individual components of foetal testicles was described in the investigated period of intrauterine development; special attention was paid to those morphological components which are closely related with their functional activity in the course of development. The results of this study will contribute to the enrichment of theoretical principles of veterinary embryology, physiology, endocrinology and andrology.