This study was designed to develop a version of the stop task, a putative measure of behavioral inhibition, for use in rats and to assess the effects of d-amphetamine (AMP) and alcohol (ALC). The stop task provides a quantitative index of the ability to inhibit a response that has been initiated. Rats (N = 11) were tested after intraperitoneal injections of AMP (0.125, 0.25, 0.5, 1.0 mg/kg) and ALC (250, 500, 750 mg/kg). AMP improved the ability to inhibit responses only in rats with relatively poor inhibitory performance at baseline. ALC impaired inhibition at doses that did not affect simple reaction time. The results support the sensitivity, reliability, and validity of the procedure as a measure of behavioral inhibition in rats and are highly concordant with a parallel study conducted with humans.