Lipofuscin has been of interest in dementia of Alzheimer's type (DAT), because of the hypothesis that dementia is a kind of premature ageing. The results of studies on intraneuronal lipofuscin content in DAT are inconsistent. At present no data on intraneuronal lipofuscin in dementia with Lewy bodies (DLB) are available. The amount of lipofuscin in the neurons of the inferior olivary nucleus of 10 brains of DLB patients, 10 of age-matched DAT patients, and 10 of age-matched controls has been measured microfluorometrically. The intraneuronal lipofuscin content in the DLB patients was significantly lower than in the DAT patients and controls. This finding may indicate a general alteration of neuronal cell metabolism in DLB, e.g. a defect of mitochondrial DNA, not confined to neurons developing Lewy bodies.