Paired blood samples were collected simultaneously from the jugular vein and from the carotid artery of ovariectomized sheep every IS min for several hr each day. All blood samples were assayed for LH and prolactin by radioimmunoassay. Selected samples were also assayed for GH and for total adrenal corticoids. Cranial output (ng/ml) for a pair of samples was denned as the venous concentration (ng/ml) minus the arterial concentration (ng/ml) and was assumed to reflect hormone release by the pituitary and equilibration of circulating hormone with the extravascular spaces of the head. Arterial LH fluctuated widely in ovariectomized ewes showing very regular peaks occurring at about hourly intervals. Cranial output of LH revealed that the pulsatile discharges of LH from the pituitary were both very large and very brief. Venous LH levels were sometimes 3–4–fold greater than arterial levels in the paired sample. Furthermore, it was estimated that these hourly discharges lasted only about 5 min. Arterial levels of prolactin, LH and total adrenal corticoids fluctuated independently and within sample correlations between hormones were all near zero. Cranial output of prolactin indicated a release pattern more prolonged and less pulsatile than for LH. Cranial output measurements for total adrenal corticoids suggested uptake of hormone by cranial tissues during the initial stages of peak circulating levels and subsequent movement of hormone from these tissues back into the circulation as arterial levels declined after the peak.(Endocrinology91: 738, 1972)