The effect of aging on 5-HT1A receptor binding in several forebrain areas associated with the basal forebrain cholinergic system was investigated in rats of 3-, 24- and 30-months-old by receptor autoradiography and biochemical binding assay using [3H]8-OH-DPAT as a ligand. Autoradiographic measurements demonstrated a marked region-specific decline of ligand binding in: (i) regions of the basal forebrain cholinergic cell groups, i.e. the medial septum, diagonal band nuclei and magnocellular nucleus basalis, (ii) the frontal and parietal neocortex and (iii) the dentate gyrus of the hippocampus. No change or only a slight decrease of the 5-HT1A receptor density was found in other areas investigated: the CA1 and CA3 sectors of hippocampus, the cingular and perirhinal cerebral cortex and the lateral septum. The autoradiographic findings were substantiated by the biochemical binding assay, which revealed a comparable loss of 5-HT1A receptor in the hippocampus and neocortex at the age of 30 months. The results clearly show that with increasing age the decrement of 5-HT1A receptor binding in the rat forebrain is remarkably region-selective and particularly affects the cholinergic cell groups that innervate cortex and hippocampus. This phenomenon appears to be especially significant in relation to the neuronal substrates underlying the age-related alterations of mood and cognition.