Studies were conducted to determine if the hypothermic effects of barbiturates were responsible for their ability to suppress luteinizing hormone (LH) secretion in rats following ovariectomy or treatment with gonadal steroids. In both ovariectomized rats and rats treated with estradiol and progesterone, pentobarbital caused a marked hypothermia and blocked LH hypersecretion. In ovariectomized rats, the LH-suppressing effects of pentobarbital could be prevented by maintaining normal core body temperature. However, in steroid-treated rats, the maintenance of normal core body temperature did not prevent the pentobarbital-induced blockade of the steroid-induced LH surge. These data indicate that the pentobarbital-induced reduction of LH secretion in ovariectomized rats is temperature-dependent, while its blockade of the steroid-induced LH surge is not. Additionally, this study provides further evidence for the differential neuronal regulation of LH secretion following ovariectomy and during the steroid-induced surge in LH.