Interleukin-1 (IL-1)-1) is a pluripotent immunomodulatory cytokine that has an initiating role in cellular and humoral immunity in the periphery. Il-1 is overexpressed in Alzheimer brain, and this overexpression is directly related to plaque formation and progression, nonsensical growth of dystrophic neurites, and neuronal overexpression of acetylcholinesterase. IL-1 has a number of actions relevant to Alzheimer's disease, including excessive expression of neuronal Abeta precursor protein and other plaque-associated proteins, and induction of astrocyte activation and astrocytic overexpression of S100B. These latter events may be related to the overgrowth of dystrophic neurites in neuritic plaques, a necessary event for conversion of diffuse Abeta deposits into the neuritic amyloid plaques diagnostic of Alzheimer's disease. Four new genetic studies underscore the relevance of IL-1 to Alzheimer pathogenesis, showing that homozygosity of a specific polymorphism in the IL-1A gene at least triples Alzheimer risk, especially for an earlier age of onset and in combination with homozygosity for another polymorphism in the IL-1B gene.