The effects of placebo, triazolam (2.0, 4.0 and 8.0 micrograms/kg) and ethanol (0.25, 0.5, 1.0 g/kg) on perceptual-motor performance were examined using a visual pattern matching-to-sample procedure in which pattern size and comparison stimulus discriminability were systematically varied. Baseline response rates and accuracy increased as the discriminability of the comparison stimuli increased. At the highest dose, both drugs decreased response accuracy. This disruption of accuracy was attenuated by increasing the discriminability of non-matching stimuli. Triazolam produced dose-related decreases in response rate while ethanol produced only slight decreases at the highest baseline rates of responding. Thus, triazolam produced response rate slowing at relatively lower doses than ethanol.