Central injection of peptide YY (PYY) elicits a powerful feeding response with a short latency in satiated rats. Because of this effect, PYY has been implicated as a neurochemical signal in bulimia nervosa. Serotonin agonists and opioid antagonists induce anorectic effects upon feeding behavior in humans and animals. Therefore, to investigate a possible interaction between PYY-induced eating and these anorexigenic agents rats were given injections of either naloxone (100 μg/3 μl, ICV, and 10 mg/kg, SC), fluoxetine (3-30 μg/3 μl and 5-10 mg/kg, IP), or clomipramine (3-30 μg/3 μl and 5-10 mg/kg, IP) prior to fourth ventricular injections of PYY (15 μg/18 μl). Central and peripheral naloxone and IP but not central injections of fluoxetine blocked PYY-induced intake. Clomipramine had no effect. This suggests that PYY-stimulated feeding may require the action of endogenous opioids and may be inhibited by serotonergic function. © 1993.