The effectiveness of a recently synthesized corticotropin releasing factor (CRF) antagonist, alpha-helical CRF9-41, in reversing the locomotor activating and proconflict effects of CRF was evaluated. The CRF receptor antagonist (50, 100 and 200 micrograms, i.c.v.) produced a dose-related attenuation of the response-suppressing effects of CRF in a conflict model of anxiety. The antagonist also effectively suppressed the marked locomotor activation produced by CRF. No discernible intrinsic effects on behavior were noted when the antagonist was administered alone. These results suggest that the behavioral effects of CRF are receptor-mediated phenomena and point to the potential usefulness of a CRF antagonist in understanding the function of endogenous CRF in mediating responses to stressful stimuli.