Local inflammatory processes surrounding the amyloid plaques contribute to the progression and acceleration of the Alzheimer's disease (AD)-related neurodegeneration. Interleukin-6 (IL-6) is an inflammatory cytokine with possible involvement in the local immune response occurring in the central nervous system of AD patients. We tested the hypothesis as to whether a genetic polymorphism of the IL-6 gene (IL-6) modifies the age at onset and risk for sporadic AD. Our results support an association of the C allele of the IL-6 genotype with a delayed initial onset and reduced disease risk and indicate that genetically determined alterations of the immune response may modify the course of AD.