Concentrations of hypoxanthine, xanthine, uric acid and creatinine were measured in CSF of patients suffering form presenile and senile dementia of Alzheimer type (PDAT, SDAT) and multi infarct dementia (MID) and in a reference group of young neurotic patients. There was no difference in hypoxanthine concentration, but there was a marked elevation of xanthine concentration in each dementia group, independent of the type of dementia. There was a significant elevation of uric acid in SDAT and MID but not in PDAT. The concentration of uric acid was higher in MID than in SDAT. There was a higher level of creatinine in the dementia groups, but no difference was seen among the dementia groups. These results are discussed in order to better interpret the etiology and the differentiated diagnosis of the types of dementia.