The ovary not containing the corpus luteum was removed from each of 52 ewes on Day 8 of the cycle. These animals were then allocated to one of the following groups. Group 1: (control) received no further treatment. Group 2: the contralateral uterine horn, i. e. located on the side opposite to the corpus luteum, was removed. Group 3: the ipsila-teral uterine horn, i. e. located on the same side as the corpus luteum, was removed. Neither unilateral ovariectomy alone (Group 1) nor the removal of the contralateral horn (Group 2) affected the length of the post-operative estrous cycles. In contrast, extirpation of the Ipsilateral uterine horn (Group 3) resulted in a significant extension of the estrous cycle and thus of the life-span of the corpus luteum. The results suggest that the ovaries of the cyclical sheep are probably affected by the uterus in a local manner.