The effects of the muscarinic agonist, arecoline, on the concentration of homovanillic acid (HVA) in the cerebrospinal fluid of patients with Alzheimer's disease (AD) and controls were examined. Patients and controls received intravenous infusions of arecoline and a lumbar puncture was performed four hours after the infusion began. Arecoline induced a significant increase in the concentration of HVA in cerebrospinal fluid of Alzheimer's disease patients (p < .01) but not in controls. The differential HVA response to a muscarinic agonist in Alzheimer's disease is suggestive of an alteration in muscarinic receptor response. This finding may have potential implications for the pathophysiology and treatment of Alzheimer's disease.