Drugs, such as sodium mercaptoacetate and methylpalmoxirate, which block fatty acid oxidation at different levels in the metabolic pathway, stimulate feeding. It is well known that selective centrally induced stimulation of dopamine, serotonin (5-hydroxytryptamine, 5-HT) and beta-adrenoceptors, or inhibition of the opiatergic system substantially decrease food intake in rats trained to eat 4 h a day. The results of the present study show that centrally acting dopaminergic and serotoninergic anorectic drugs, the opiate receptor antagonist naloxone, the alpha-adrenoceptor blocking drug phentolamine, and peripherally administered 5-HT counteract the overeating induced by mercaptoacetate. Comparing these effects to those described in 2-deoxy-D-glucose- and insulin-induced feeding, our data support the proposition that distinct neural circuits are involved in the hyperphagic responses to diverse metabolic stimuli.