The effects of cholecystokinin octapeptide (CCK-8), and its antagonist proglumide, upon conditioned behavior in the rat was studied. First, the effects of CCK-8 and proglumide upon passive avoidance behavior was investigated. Rats were trained to avoid a darkened chamber by presenting electrical footshock (two seconds of intensity levels) inside the chamber. Directly following the footshock, injections of CCK-8 or proglumide were given, with avoidance behavior measured 24 hours following the injection. CCK-8 was found to produce reductions in the passive avoidance latency at doses ranging from 30 ug/Kg to 500 ug/Kg. This effect was found to be dependent upon the current intensity used during conditioning. The CCK-8 effect was found when the current was at 0.25 mA, but at no other current setting tested. Proglumide (5 mg/Kg) was found to block the CCK-8 effect upon passive avoidance behavior. A lower dose of proglumide (2 mg/Kg) was found to produce reductions in the passive avoidance latency. These results suggest that CCK-8 may play a role in passive avoidance conditioning in rats. The effects of CCK-8 upon an appetitively conditioned behavior were then investigated. Rats were trained to locate and drink from a drinking tube that contained a 10 percent sucrose solution. Following 30 seconds exposure to the solution, injections of CCK-8 were given, with the latency to begin drinking from the tube measured 24 hours later. CCK-8 was found to produce increases in the latency to begin drinking, at doses of 20 ug/Kg and 100 ug/Kg. CCK-8 also produced a reduction in the amount of sucrose solution consumed during the test period. When CCK-8 was given following exposure to regular tap water, no increase in drinking latency or reduction in consumption was found. These results suggest that CCK-8 can act as an aversive stimulus and is capable of producing conditioned taste aversions. The results of this dissertation project demonstrate that CCK-8 can influence the acquisition of conditioned behavior in the rat when the octapeptide is paired with the presentation of an unconditioned stimulus (shock or sucrose).