Besipirdine hydrochloride (HP 749) is an indole-substituted analog of 4-aminopyridine. Besipirdine enhances both cholinergic and adrenergic neurotransmission in the central nervous system. The present study examined the efficacy and tolerability of two doses of besipirdine (5 and 20 mg b.i.d.) in 275 patients with Alzheimer disease during 3 months of treatment and for 3 months after withdrawal of treatment. Assessment after withdrawal of treatment was used in an effort to distinguish persistent efficacy attributable to a neuroprotective mechanism from reversible symptomatic efficacy. Besipirdine was generally well tolerated. The level of performance on the cognitive subscale of the Alzheimer Disease Assessment Scale (ADAS-Cog) was sustained during 3 months of treatment with besipirdine, whereas some deterioration in the performance of patients treated with placebo was observed over the same period. The small difference between active and placebo treatment groups approached, but did not reach statistical significance in the primary intent-to-treat analysis (p = 0.067); analysis of patients who completed all assessments was supportive (p = 0.031). Global ratings using the Clinician Interview-Based Impression of Change did not detect a besipirdine treatment benefit, possibly because of an adverse effect on mood and behavior in some patients. A high ratio of adrenergic to cholinergic potency may have resulted in the adverse effects of besipirdine and hence its failure to support the hypothesis that multiple neurotransmitter treatment may be more efficacious than monotherapy. The efficacy apparent on the ADAS-Cog after 3 months of treatment did not persist 3 months after withdrawal of treatment, suggesting that the benefit was symptomatic. This study provides a practical example of the use of treatment withdrawal assessment to distinguish neuroprotective from symptomatic efficacy.