Neuropsychologists need more sensitive methods to detect and measure recreational drug use in both research and clinical settings. In a study comparing the sensitivity of information processing tasks and neuropsychological instruments to detect early HIV-related cognitive decrements, 18 of 129 subjects tested positive for recreational drugs. Sixteen of these 18 subjects had elevated false alarm rates on one of the information processing tasks, the vigilance task. Another 45 subjects who tested negative for recreational drugs also had elevated false alarm rates. Neuropsychological measures of premorbid functioning, attention, speed of information processing, and manual dexterity were lower in the high false alarm subjects than in the remaining 66 drug-negative, low false alarm subjects. These results suggest that a high false alarm rate may reflect long-standing cognitive disturbances and the effects of drug use. The vigilance task may be a sensitive and efficient screening tool for recreational drug use.