At low doses Ro 64-6198 is anxiolytic in several neophobic tests, including the marble burying test in mice, the elevated plus maze in rats and the open field test in rats. In the marble burying test, at 1 mg/kg, i.p., Ro 64-6198 produces a decrease in the number of marbles buried, without altering locomotor activity, indicating a decrease in neophobia and anxiety. Ro 64-6198 selectively increases the number of open arm transitions and time spent in the open arms of the elevated plus maze at doses of 0.32-3 mg/kg, i.p., without affecting closed arm transitions or locomotor activity in the closed arms. In the open field test, Ro 64-6198, at doses of 0.32-3 mg/kg, attenuates the inhibition of exploration that results from the stress of a novel environment.