Levels of dopamine and serotonin, and of their precursors and metabolites, were measured in the nucleus basalis of Meynert (nbM) of patients with Alzheimer's disease and control patients. [3H]Spiperone binding to membrane homogenates of the nbM, indicative of both dopaminergic and serotonergic receptors, was also measured. The nbM from patients with Alzheimer's disease showed significant decreases in both spiperone binding and in the levels of dopamine and serotonin but no decrease in either tyrosine or tryptophan levels. These data indicate a loss of both dopaminergic and serotonergic synapses in the nbM of patients with Alzheimer's disease.