The pre- and postovulatory levels of oestradiol and progesterone were measured in seven brain areas, peripheral fat, muscle tissue and blood plasma in 49 immature female rats which had been given an injection of 4 IU PMSG (Pregnant Mare Serum Gonadotropin) on the 25th day of life. We observed a uniform decline in oestradiol concentration in all the areas of the postovulatory rat. The highest mean concentrations of oestradiol pre- and postovulatory were found in the hypothalamus and the striatum (260 +/- 26, 110 +/- 11, 200 +/- 39 and 75 +/- 13 pg g-1, respectively). The levels of progesterone showed variable increases in all the areas postovulatory. The highest postovulatory concentration was found in the cerebral cortex (29 +/- 2.0 ng g-1) where the increase was six-fold greater than the increases in any of the other areas compared to preovulatory values. The hypothalamus contained high progesterone levels at both times (3.5 +/- 0.68 ng g-1 and 27 +/- 5.2 ng g-1) compared to other areas. We conclude that the female rat brain exhibits differences in the distribution of oestradiol and progesterone both pre- and postovulatory. Since the levels in different brain areas to a large extent varied independently we suggest different uptake mechanisms and/or different binding capacities in various regions of the rat brain.