Food intake after fourth intracerebroventricular (icv) injections of bombesin (BBS) was measured in intact rats. BBS injections (greater than or equal to 10 ng) reliably suppressed chow intake in 17-h food-deprived rats. Systemic injections of BBS (50 ng) had no effect on food intake. These data indicate that BBS can act directly on caudal brain stem site(s) to inhibit food intake. The behavioral specificity of fourth icv BBS was evaluated by measuring the effects of fourth icv BBS injection on water intake by 17-h water-deprived rats in the presence and absence of food. Fourth icv injections of BBS in doses greater than 10 ng suppressed 30-min and 2-h water intake relative to saline injection when food was available in the home cage. In contrast, when food was not present during the 2-h intake test, fourth icv injections of BBS had no effect on water intake. This suggests that the inhibition of water intake was secondary to the effects of BBS on food intake. Lastly, sucrose (0.1 M) was paired with fourth icv BBS (50 ng), fourth icv saline, and intraperitoneal LiCl (1.5 meq/kg) in three groups of naive rats, and sucrose preference was subsequently measured. Rats that received injections of either saline or BBS preferred sucrose during the 24-h two-bottle test, and their preference ratios were significantly greater than those of the LiCl-injected rats. The role of afferent signals elicited by fourth ventricle BBS administration in the control of food intake is discussed.