To investigate the immune response to amyloid beta-peptide (Abeta: Abeta40 and Abeta42) in peripheral human blood, sera were obtained from 36 patients with Alzheimer's disease (AD) and 34 age-matched controls. ELISA assays were used to measure antibody concentrations to Abeta-peptides. T cell response was assessed using a lymphoproliferation assay. Both AD and control subjects had low and variable concentrations of antibodies against Abeta (predominantly IgG1). The mean antibody to Abeta concentrations did not differ between groups. No specific T cell response to Abeta-peptides was detected. Natural levels of antibodies to Abeta in peripheral blood are present in all human subjects and are unlikely to be useful in the identification of patients who would respond to potential AD immune therapy. Specific cellular immune responses to Abeta in human blood were not detected.