Amino acids were measured in nine cases of dementia of the Alzheimer type, 10 cases of multi-infarct dementia, and 10 healthy controls. The severity of dementia was examined using mini-mental state test (MMST). Amino acid analysis (41 kinds) in the cerebrospinal fluid (CSF) and serum was performed in the Special Reference Laboratories. In the dementia of the Alzheimer type group, methionine and alanine concentrations in the CSF were significantly increased, and the CSF/serum ratios for both the alanine and glycine concentrations were significantly increased, in comparison with the healthy control group. In the multi-infarct dementia group, glycine, methionine, threonine, phenylalanine, and citrulline concentrations in the CSF were all higher than in the healthy control group. Significant negative correlations were found between the MMST score and the alanine, urea, arginine, and alpha-aminobutyric acid concentrations in the CSF. The number of amino acids which exhibited abnormality in dementia of the Alzheimer type and multi-infarct dementia was greater in the present study than in previous reports.