Female ovariectomized (OVX) and sham-OVX rats were trained in a task designed to assess sustained attention. After achieving asymptotic performance, OVX rats did not exhibit the impairment in performance over blocks of trials (i.e., the vigilance decrement) observed in sham-OVX rats. Furthermore, OVX rats' performance over blocks of trials was unaffected by the normally detrimental effects of a visual distractor. 192 IgG-saporin-induced lesions of basal forebrain cholinergic neurons resulted in similar impairments in the performance of OVX and sham-OVX rats. The acute, but not chronic, administration of 17beta-estradiol attenuated the lesion-induced decrease in the relative number of hits to longest signals exclusively in rats with intact ovaries. These findings indicate that the variables contributing to the potential therapeutic effects of estradiol remain poorly understood.