GABAB and GABAA binding sites were evaluated by quantitative autoradiography of 3H-GABA binding in superior frontal gyrus of persons who died with dementia of the Alzheimer's type (DAT) and of age-matched normal controls. Scatchard analysis and competition studies disclosed 48 to 68% and 25% decrements in receptor density (Bmax) for GABAB and GABAA receptors, respectively, in layers II, III, and V of DAT frontal cortex as compared with controls. No significant difference in affinity (KD) for either GABAA or GABAB receptors was found. Our data may reflect multisystem pathologic involvement in DAT neocortex.