Correlation between estradiol to progesterone ratio and gene expression in small and medium sheep follicles. Follicular fluid was pooled according to follicle diameter: small (≤ 2.0 mm) and medium (2.1-4.0 mm). After cells were separated by centrifugation, duplicate aliquots (200 μl total volume) of follicular fluid were analyzed by RIA without extraction. Estradiol and progesterone concentrations were determined for each sample, and the ratio of estradiol to progesterone was calculated, then analyzed for correlation to FSHR or LHR gene expression. The FSHR-2 variant had the highest correlation (R = 0.4) to the E:P ratio compared to other FSHR variants. The E:P was inversely correlated to LHR expression in small follicles (R = −0.41), and FSHR-1 expression in medium follicles (R = −0.41). Data are expressed as correlation (R) values.