In the present study the frequency and magnitude of the release of 5-Hydroxyindoleacetic Acid (5-HIAA) was measured from the anterior hypothalamus of ovariectomized (OVX) and OVX rats treated with estradiol (E2). Female, Holtzman strain rats were maintained on a photoperiod of 14 H light from 0100 to 1500 H and experiments performed from 0900 to 1700 H. Animals exhibiting four-day estrous cycles (250-300 gms) were OVX (20 days recovery) and a push-pull-cannula (PPC) implanted and stereotaxically aimed at the SCN region in the anterior hypothalamus. Following a 7-10 day recovery push-pull-perfusion (PPP) experiments were performed on either OVX females or on OVX females in which a silastic E2 implant (150 micrograms E2/ml. sesame oil), was placed sc 48 H prior to PPP. In other experiments progesterone (P4) was perfused in a pulsatile manner over the SCN region of the anterior hypothalamus. The overall average 5-HIAA release in the OVX treated rats (548 +/- 358 pg/10 min.) was similar to that in the OVX E2 group (694 +/- 148 pg/10 min). The average period of 5-HIAA release was (48.2 +/- 5.5 min) in the OVX group and (56.0 +/- 9.8 min) in the OVX E2 group. These results indicate that exposure of long term OVX rats (20 days) to E2 has no effect on the release or period of 5-HIAA release from serotonergic terminals concentrated in the SCN of the anterior hypothalamus.(ABSTRACT TRUNCATED AT 250 WORDS)