This study was undertaken to determine the patterns of estrogen and progestin secretion by the adrenal and the ovary and to relate these to the levels of steroids and gonadotropins found in peripheral plasma. A total of 70 rats were used in this study. Adrenal venous (ADVB) and ovarian venous blood (OVB) were collected by concurrent cannulation and peripheral blood (PB) was obtained from the abdominal aorta. Estrone (E1), estradiol (E2), PROGESTERONE (P) and 17alpha-hydroxyprogesterone (17alpha-OHP) were measured by radioimmunoassay. The concentration of E2 in general was higher in ADVB than in OVB. Although increased levels of E2 in ADVB were found on the afternoon of proestrus (1527-2634 pg/ml), they were not significantly different from those recorded at other times. In contrast E2 in OVB was lowest at 1000-1200 hr of estrus (225 pg/ml) and highest at 1000-2000 hr of proestrus (1190-1605 pg/ml). The E2 in PB followed the pattern seen in OVB; the values ranged from 80-211 pg/ml. P concentration in general was higher in ADVB than in OVB. The lowest concentration of P in ADVB was between 0200-0400 hr of estrus (183 ng/ml) and the highest between 1400-1600 hr of proestrus (580 ng/ml) and 1000-1200 hr of estrus (591 ng/ml). The lowest concentration of P in the OVB was between 1600-1800 hr of diestrus (42 ng/ml) and the highest between 0200-0400 hr of estrus (466 ng/ml). In the PB, P reflected changes in adrenal as well as ovarian secretion; the values ranged fron 7-25 ng/ml. E1 in ADVB was in general lower than in OVB, and there were no significant changes at any stage of the cycle. In the OVB, however, E1 showed a pattern similar to that of E2. Levels of E1 in PB were very low and failed to show any significant changes. 17alpha-OHP was high in ADVB, although there were no significant changes during the cycle; PB levels also did not show any significant changes. In the OVB a peak of 17alpha-OHP was recorded between 0200-0400 hr on the day of estrus. The LH and FSH levels showed increases after 1600 hr on the day of proestrus and this was in agreement with earlier studies. Since the adrenal secretes all of the 4 steroids studied, it is reasonable to assume that it does exert some effect in the pituitary-gonadal axis. A role of adrenal P for the facilitation of the preovulatory LH release has been indicated and the increased secretion of adrenal P between 1400-1600 hr of proestrus supports this possibility.