A stylus-tracking task and a task devised by the General Motors Corporation were examined for their prospective value as alcohol ignition interlock systems. 16 Ss were extensively practiced on the 2 tasks before being tested during the absorption, peak, and elimination phases of the blood alcohol cycle at BACs of 0.05%, 0.10%, and 0.05%. While significant decrements in performance were found in both tasks at 0.10% BAC, only the stylus-tracking task showed useful test discrimination between Ss at BACs of 0% and 0.10%.