Postprandial administration in the rat of a wide variety of drugs, peptides and toxins suppresses future consumption of a meal of previously unfamiliar but otherwise attractive saccharin-flavored solution. Since the intensity of this conditioned flavor aversion in the rat is sensitive to plasma stress hormone levels, the present study examined the effects on flavor conditioning of corticotropin-releasing factor, a peptide known to be involved in behavioral and hormonal responses to stress. In two-bottle water vs. saccharin choice tests, CRF (0.5 microgram ICV) increased significantly the consumption of saccharin solution following a single saccharin/CRF pairing, while a tenfold larger dose of CRF (5 micrograms ICV) abolished saccharin intake following two saccharin/CRF pairings. Hence, exogenous CRF is capable of inducing both flavor preference and aversion in a dose- and situation-dependent manner. Further, direct neurotropic actions of CRF probably subserve its aversive effect since dexamethasone pretreatment weakened but did not prevent CRF-induced conditioned taste avoidance. These results suggest that at low doses CRF can produce arousal actions that result in taste preference and at higher doses produces aversive effects that are reflected in taste avoidance.