The effects of acute administration of chlordiazepoxide (2.5 and 5.0 mg/kg, i.p.), nicotine (0.05,0.1 and 0.4 mg/kg, s.c.) andd-amphetamine (0.5 and 1.0 mg/kg, i.p.) on rat potentiated startle were investigated. Chlordiazepoxide, 2.5 and 5.0 mg/kg, attenuated potentiation of startle, indicating an anxiolytic profile, although the effect of the higher dose was less marked and was accompanied by a reduction in overall startle response, probably reflecting drug-induced sedation. Nicotine at doses of 0.05 and 0.4 mg/kg had no significant effects in this test. However, 0.1 mg/kg nicotine eliminated potentiation of startle (in two separate experiments), an action comparable to that of 2.5 mg/kg chlordiazepoxide.d-Amphetamine at doses of 0.5 and 1.0 mg/kg did not significantly influence potentiation of startle. The results suggest that nicotine has an anxiolytic profile in the potentiated startle paradigm which is not due to its psychostimalant properties.