Intravenous immunoglobulin (IVIg) has been proposed as a potential agent for Alzheimer's disease (AD) immunotherapy because it contains antibodies against beta-amyloid (Aβ). We carried out an open label dose-ranging study in 8 mild AD patients in which IVIg was added to approved AD therapies for 6 months, discontinued, and then resumed for another 9 months. Infusions were generally well-tolerated. Anti-Aβ antibodies in the serum from AD patients increased in proportion to IVIg dose and had a shorter half-life than anti-hepatitis antibodies and total IgG. Plasma Aβ levels increased transiently after each infusion. Cerebrospinal fluid Aβ decreased significantly at 6 months, returned to baseline after washout and decreased again after IVIg was re-administered for an additional 9 months. Mini-mental state scores increased an average of 2.5 points after 6 months, returned to baseline during washout and remained stable during subsequent IVIg treatment. Our findings confirm and extend those obtained by Dodel et al. [Dodel, R.C., Du, Y., Depboylu, C., Hampel, H., Frolich, L., Haag, A., Hemmeter, U., Paulsen, S., Teipel, S.J., Brettschneider, S., Spottke, A., Nolker, C., Moller, H.J., Wei, X., Farlow, M., Sommer, N., Oertel, W.H., 2004. Intravenous immunoglobulins containing antibodies against beta-amyloid for the treatment of Alzheimer's disease. J. Neurol. Neurosurg. Psychiatry 75, 1472–1474] from a 6-month trial of IVIg in 5 AD patients and justify further studies of IVIg for treatment of AD.