To elucidate the influence of the alpha1-antichymotrypsin (ACT) polymorphism on Alzheimer-type neuropathological changes and the development of sporadic Alzheimer's disease (AD), we studied the relationship between the ACT polymorphism and the severity of Alzheimer-type neuropathological changes in the brains from AD patients and nondemented subjects. There was no association of the ACT polymorphism with Alzheimer-type neuropathological changes in AD or nondemented individuals. ACT polymorphism was not associated with the development of AD. These results remained nonsignificant when the ACT genotype groups were divided into subgroups according to the apolipoprotein E (ApoE) epsiolon4 status. Our study shows that the ACT polymorphism has no effect on Alzheimer-type neuropathological changes or the development of AD, either alone or in combination with ApoE epsiolon4.