The integrity of the cortical cholinergic input system is necessary for attention performance. This experiment tested hypotheses concerning the lateralized contributions of cortical cholinergic inputs to attention performance by assessing the effects of unilateral lesions of basal forebrain cholinergic neurons on sustained attention performance. Loss of right-hemispheric cortical cholinergic inputs impaired the rats' ability to detect signals but did not affect nonsignal trial performance. Conversely, loss of left-hemispheric cortical cholinergic inputs increased the number of false alarms in nonsignal trials. These data correspond with hypotheses about the mediation of detection processes primarily by right-hemispheric circuits and executive aspects of attention performance by left-hemispheric systems. Cortical cholinergic inputs represent a major component of the brain's lateralized attention systems.