In Experiment 1, four groups ofmale rats were given a session as an intruder in either aggressive (i.e., alpha) or nonaggressive colonies of conspecifics and later received either a 2-h exposure to the odors of the alpha colonies or an exposure-control session with the odors of a nonalpha colony. Two additional groups of rats that had been attacked and defeated by alpha residents were later given a 12-h exposure session with alpha-colony odors or nonalpha-control odors. Twentyfour h after the colony-intruder session, all subjects were given a single 6.5-mA shock from a prod with alpha-colony odors present in the bedding ofthe test chamber. Attacked rats that had been given exposure-control sessions showed significantly less prod burying and greater freezing than nondefeated subjects. This implies that the alpha-colony odors elicited conditioned fear. In contrast, the attacked subjects that had been given apretest exposure session with alpha-colony odors showed significantly more prod burying and significantly less freezing. This suggests that the alpha-odor exposure resulted in the extinction of fear to these odors. Furthermore, the 12-h exposure to alpha-colony odors was found to be more effective in reducing fear-mediated responses than was the 2-h exposure. In Experiment 2, three groups of rats were exposed to a cat while they were in a protective cage; later they were given a 12-h exposure session with cat odors, a 12-h exposure-control session with no cat odors, or no exposure treatment. Compared with the two control groups, the subjects that were exposed to cat odors showed less freezing during subsequent prod-shock tests in the presence of cat odors, but they did not show prod burying. The reported changes in fear-mediated reactions to the odors of conspecifics and a predator are discussed in terms of both associative and nonassociative processes.Over the past several years, considerable research has examined the influence that both laboratory and natural stressors, and their relatedodors, have on subsequent fearmediated responses producedby the use of the prod-shock procedure (see Williams, 1987aWilliams, , 1989, for reviews). This procedure, which has been extensively studied by Pinel and his colleagues (e.g., Pinel & Treit, 1978, 1981, consists of administering a single electric shock from a prod that is mounted on the wall of achamber with movable beddingmaterialon the floor. Whentested withthis procedure, rats typically show abrief freezing reaction foIlowing the prod shock, and then they bury the prod with the bedding material. AlthoughPinel has interpretedthis type of prod burying to be a conditioned defensive response (Pinel & Treit, 1978, 1981Treit, 1985), others have claimed that it is an example of shock-elicited spraying or burrowing (Fanselow, Sigmundi, & Williams,