In our previous study, elderly leprosy patients showed a low prevalence of senile dementia of the Alzheimer type, but the frequency of apolipoprotein E (APO-E) epsilon 4 was elevated in non-demented elderly leprosy patients. Recent study has shown that Alzheimer's disease risk associated with APO-E epsilon 4 is significantly increased by the alpha 1-antichymotrypsin (ACT) genotype AA. Therefore we examined an association between ACT polymorphism and the APO-E epsilon 4 allele in 350 leprosy patients. None of our data showed an association of ACT genotype and APO-E epsilon 4 allele in leprosy patients. The allelic frequencies of the ACT gene did not differ even between demented patients with leprosy and age-matched controls. Our present data suggest that ACT polymorphism is not associated with the increased frequency of APO-E epsilon 4 in leprosy patients.