It has been suggested that inflammation may be a possible cause of Alzheimer's disease (AD). Increased anti-NGF autoantibody levels and increased NGF frequency in serum have previously been associated with inflammatory responses. In this study no changes in anti-NGF autoantibody titers or in NGF frequency were detected in sera of AD patients, suggesting that they are not involved in the neuroimmunological mechanisms underlying AD. There were neither age-associated changes in NGF frequency in sera of four groups of normal subjects between 18-91 years of age. In contrast, anti-NGF autoantibodies were significantly increased in sera of the 31-45 yr age group.