CYF rats were anesthetized on various days of the 4-day cycle and blood samples were collected at 5-min interals from the ovarian vein before and after i.v. administration of 5 micrograms/100 g BW of luteinizing hormone (LH). Ovarian venous outflow, blood pressure and hematocrit were continuously recorded, and from the blood samples progesterone (P) and 17 beta-estradiol (E2) were determined by radioimmunoassay (RIA). Ovarian blood flow and P secretion showed a parallel increase on Day 1 (estrus), on Day 2, and on the afternoon of Day 4 (proestrous). LH increased ovarian blood flow each day of the cycle together with P and E2 secretion; however, no relationship was seen between the initial value of hormone secretion and the LH-induced increase of ovarian blood flow. Inhibition of hormone secretion by cycloheximide prevented the LH-induced increase of ovarian blood flow; moreover, a decrease in ovarian blood flow parallel with the diminution of hormone secretion was observed. Indomethacin pretreatment abolished the hyperemic effect of LH and partially inhibited the LH-induced increase of hormone secretion. Propranolol blocked the LH-induced increase of ovarian blood flow and blunted the effect of LH on hormone secretion. It was concluded that in LH-induced hyperemia, cAMP, prostaglandins and other vasoactive metabolites released during the process of hormone synthesis, and also a beta-adrenergic mechanism, are involved in the regulation of ovarian blood flow.