To test the hypothesis that hypothalamic β-endorphin levels were related to the body weight changes occurring with ovarian steroid treatments, 80 adult female Sprague-Dawley rats were ovariectomized and allowed to recover for 7 days. Four treatment groups of 20 each were subjected to daily injections for 14 days with A) oil, B) β-estradiol benzoate (2µg), C) β-estradiol benzoate (2µg) plus progesterone (5mg), or D) progesterone (5mg). Weight gain was significantly (p < 0.01) lower in the estrogen group when compared to the control, estrogen/progesterone, or progesterone groups. The estrogen/progesterone-treated group gained significantly less weight than either the control or progesterone group. A significant (p < 0.05) decrease in food intake was also observed in the estrogen and estrogen/progesterone groups when compared to the control and progesterone groups, but not between each other. The progesterone-treated group was not significantly different from the controls in either weight gain or food intake. Hypothalamic β-endorphin (ng/mg protein) concentrations were significantly (p < 0.05) higher in the estrogen- and estrogen/progesterone-treated groups compared to the control and progesterone groups. Again, much like the weight gain, food intake, and hypothalamic β-endorphin (ng/mg protein), the estrogen and estrogen/progesterone groups had significantly (p < 0.05) heavier adrenal weights when compared to the controls and progesterone groups. There was no significant difference in plasma corticosterone levels between any of the groups. In this study, hypothalamic β-endorphin (ng/mg protein) appeared to be effected by ovarian steroid hormone treatment. Whether this is related to the weight gain also observed with the treatments remains to be determined.Ph. D.