Previous studies from this laboratory have demonstrated that a variety of psychostimulant drugs can improve the performance of rats trained in a 2-choice stimulus detection task in which the correct responses are indicated by a briefly illuminated light. To enhance the construct validity of the task for assessing sustained attention, the procedure was modified so that the precue interval across trials varied unpredictably between 3, 7, and 11 s. After training rats (N = 17) so that their baseline accuracy levels stabilized between 75% and 88% correct, their performance was assessed after administration of d-amphetamine (0.125-0.75 mg/kg sc), nicotine (0.25-0.75 mg/kg sc), and pemoline (5.0-30.0 po). At certain doses all 3 drugs induced performance improvements in mean choice accuracy and choice response time. Because the precue intervals varied unpredictably and the cue durations used to maintain the rats' baseline accuracy levels were typically short (range = 70-500 ms), the task conforms to most conditions typically required for assessing sustained attention. Results verify the proposal that psychostimulant drugs can enhance the attentiveness of animals in a fashion similar to that documented in humans.