The effect of medial basal hypothalamic lesions on plasma and pituitary melanocyte-stimulating hormone (MSH) was determined in albino rats. 32 days postoperatively, plasma levels of MSH were elevated (p < 0.05) in female rats, whereas pituitary MSH activity was the same as in controls. Male rats also demonstrated elevated plasma MSH levels (p < 0.05) when measured 23 days postoperatively. Histological evaluation of pituitaries from these animals revealed no changes in the intermediate lobe. These data suggest that MSH release from the pituitary of the albino rat is inhibited by central neural factors.