The present study evaluated the effects of adrenalectomy and chronic administration of corticosterone on the ability of CRF given intraventricularly to increase the amplitude of the acoustic startle reflex in rats. Experiment 1 showed that CRF-enhanced startle was not affected by adrenalectomy, indicating a central effect independent of the integrity of the hypothalamic-pituitary-adrenal axis. In Experiment 2, chronic injection of corticosterone augmented CRF-enhanced startle using a dose of CRF (0.25 micrograms) that normally is ineffective in increasing startle amplitude. Chronic injection of corticosterone by itself did not increase startle amplitude (Experiment 3). We suggest that the potentiation of CRF-enhanced startle by corticosterone may result from an activation of CRF in the central nucleus of the amygdala.