Previous research has shown that basal forebrain cholinergic inputs to the cerebral cortex are necessary for attentional processing. However, the key components of attention-demanding tasks for demonstrating deficits following loss of basal forebrain corticopetal cholinergic neurons are unclear. In the present experiment, rats were trained in a visual cued discrimination task with limited explicit attentional demands and then received intrabasalis infusions of the immunotoxin, 192 IgG-saporin, or saline. Postsurgically, attentional demands were increased by decreasing the signal duration or the intertrial interval or by increasing the variability of these parameters. Subsequently, rats were trained in a task that required discrimination of successively presented signals and "blank" trials with no signal presentation. Again, attentional demands were increased by manipulating signal duration or the intertrial interval. Finally, all rats were trained in a task with both the signal duration and the intertrial interval designed to increase attentional demands. Compared to sham-lesioned animals, lesioned animals exhibited deficits in signal detection only during the successive discrimination task with both the signal duration and intertrial interval shorter and variable. The present data suggest that attentional deficits following loss of cortical cholinergic inputs result from overall attentional task demands rather than being dependent on any single task parameter.