ABSTRACT: Eosinophilic leukocytes are attracted into the preovulatory follicle and regressing corpus luteum of sheep. Eosinophils produce a wide array of potent bioactive substances that could play a role in ovarian function. Circulatory eosinophils were depleted by treatment of ewes with prednisolone, thereby producing ovarian eosinopenia. Ovulation occurred in these animals. However, circulatory concentrations of progesterone during the ensuing luteal phase were less than normal. This insufficiency was attributed in part to a suppressed angiogenic response in the formative corpus luteum. Regression of the corpus luteum induced by prostaglandin F2α was not affected by administration of prednisolone. Thus, an obligatory role of eosinophils in the mechanics of ovulation and luteal regression in the sheep is unlikely.