In rats treated with gradually increasing amounts of morphine hydrochloride until they tolerated fatal doses, levallorphan precipitated acute body weight loss and elicited a variety of other typical withdrawal symptoms. Cyproheptadine markedly reduced this b.w. loss and abolished the drug-induced withdrawal syndrome. Fenfluramine also suppressed the major signs of the levallorphan-induced morphine withdrawal; however the combination of the three drugs proved to be very toxic. Since both agents interfere with different hypothalamic feeding mechanisms these results are accordant with the hypothesis of Kerr and Pozuelo (1971) that morphine dependence and tolerance are due to a functional disorganization of the hypothalamic centers concerned wit the regulation of food intake.