Thirty-two rats injected with 20 mg/kg amobarbital and 32 given placebo were run 96 trials on a black-white discrimination followed by 160 trials of reversal training. Trials to the discriminanda were equated to provide speed data to the nonrewarded stimulus (S−) as well as to the rewarded stimulus (S+). Half the Ss were changed in drug state at the onset of reversal. The drug did not affect choice behavior or differential start speed to S+ and S− in acquisition although speeds closer to the goal were affected. In contrast, during reversal amobarbital Ss made fewer correct choice responses when compared to placebo Ss and displayed less pronounced differential start speed responding to S+ and S−. In addition to the main drug effect, a change of drug state facilitated reversal.