Plasma levels of alpha1-antichymotrypsin (ACT) and interleukin-1beta (IL-1beta) were increased in patients with probable Alzheimer's disease (AD). A common polymorphism within ACT and IL-1beta genes affected plasma levels of ACT or IL-1beta, and AD patients with the ACT T,T or IL-1beta T,T genotype showed the highest levels of plasma ACT or IL-1beta, respectively. The concomitant presence of the ACT T,T and IL-1beta T,T genotypes increased the risk of AD (odds ratio: 5.606, confidence interval: 1.654-18.996) and decreased the age at onset of the disease.