The neuropeptide cholecystokinin (CCK), via the CCKB receptor, increases behaviors associated with anxiety in laboratory animals and humans. The present experiment assessed the role of endogenous CCKB function in fear-potentiated startle, a test of "anxiety" in rats. The amplitude of the acoustic startle response is potentiated if preceded by a stimulus that has been previously paired with shock. Pretreatment with the CCKB antagonist L-365,260 (0, 0.1, 1.0, and 10.0 mg/kg, IP) did not affect baseline acoustic startle amplitudes, but dose-dependently decreased fear-potentiated startle. These results indicate that the specific attenuation of fear-potentiated startle induced by L-365,260 was not due to a general decrease in motor responsivity. The present findings are consistent with the effects of CCKB antagonists in other tests measuring anxiety in animals.