The hypothalamic preoptic area (POA) was electrically stimulated through permanently implanted electrodes in 4 unanesthetized sheep. Initiation of POA stimulation was followed within 10–20 min by large increases in plasma levels of prolactin (PRL). The stimulation-induced discharges of PRL were consistently observed in both untreated and estradiol-treated castrated animals using 0.1 to 0.7 mA of applied current. Since behavioral modifications were only sometimes associated with electrical stimulation of the POA, the response appears unrelated to the stress-induced release of PR