Estradiol and progesterone concentrations in follicular fluid from different-sized sheep follicles. Follicular fluid was pooled according to follicle diameter: small (≤ 2.0 mm), medium (2.1-4.0 mm) and preovulatory (preov; ≥ 6.1 mm). After cells were separated by centrifugation, duplicate aliquots (200 μl total volume) of follicular fluid were analyzed by RIA without extraction. Progesterone concentrations were consistently higher than estradiol in small, medium and preovulatory follicular fluid pools. Data are expressed as mean ± SEM.