Progesterone, androstenedione, testosterone, estrone and estradiol were measured in the postovulatory follicle (POF) at various times up to 52 h after oculation. The 3-fold decrease in progesterone, the major constituent, which occurred over the first 15-20 h resembled the changes previously described for the enzyme, 3.beta.-hydroxysteroid dehydrogenase. At 1 h before ovulation the granulosa cells of the anteovulatory follicle (AOF) contained 50 times more progesterone than the POF granulosa fraction collected 2-3 h later. The thecal portion of the AOF had progesterone concentrations 5 times those of the POF theca, but the latter contained higher concentrations of androstenedione and estrone.