Glucose has previously been shown to improve performance on memory tasks and to ameliorate performance deficits induced by scopolamine or morphine. To test the generality of these observations, Sprague-Dawley rats were trained to alternate choices to reach an escape platform in a two-choice circular water maze. The rats attained a high level of alternation, alternating on a mean of 9 of 10 daily trials. Daily glucose injections (100 and 250 mg/ kg) failed to facilitate acquisition of the alternation. Single injections of scopolamine (0.5, 1.0, and 2.0 mg/kg), but not methylscopolamine (0.5 mg/kg), and daily injections of scopolamine (0.5 mg/kg) or morphine (5.0 mg/kg) impaired alternation performance. The scopolamine- and morphine-induced deficits in alternation behavior were not ameliorated by pretrial glucose injections at doses which have previously been found to be effective (100 and 250 mg/kg). The mechanism of glucose facilitation of memory is currently unknown. The present results show that glucose given at previously established effective doses does not activate the mechanism or produces too weak an effect to be observed in water maze alternation.