Ligand binding to alpha 1-, alpha 2- and beta-adrenergic, serotonin, benzodiazepine and GABA receptors was studied in neocortex and hippocampus of controls and patients with senile dementia of the Alzheimer-type. A selective loss of serotonergic binding sites characterised as a loss of both S1 and S2 sites was observed. The reduction in serotonin receptors did not correlate with a clinical assessment of the degree of dementia, or with the extent of Alzheimer-type neuropathological change.