Using [3H]ketanserin, a specific ligand for the 5-HT2 receptor, the amount of specific binding was measured in preparations of post-mortem frontal cortex from subjects diagnosed as suffering from dementia. A highly significant 42% loss of binding was observed which reflected a decrease in receptor density compared to psychiatrically normal controls. This was found to be independent of age in the demented patients and thus unlikely to be related to the cholinergic deficit. Measurement of 5-HT and its metabolite 5-HIAA indicated a smaller, non-significant decrease in presynaptic 5-HT function.