Associations have been reported between polymorphisms in the gene for alpha 1-antichymotrypsin (ACT) and both Alzheimer's disease (AD) and cerebrovascular disease. An A-to-G substitution at nucleotide position 1,252 of ACT that produces a methionine to valine substitution at codon 389 has been found previously in four of 32 individuals with cerebrovascular disease from a Japanese population. We genotyped 194 individuals [59 controls, 35 with non-AD-type dementia (primarily vascular) and 100 with Alzheimer's-type dementia] for this polymorphism and found none that carry this polymorphism. Therefore, the allelic association of the A1252G mutation of ACT with cerebrovascular disease may be confined to the Japanese population and is not generalizable to other populations.