Intravenous immunoglobulin infusions into Alzheimer patients have been found to provide cognitive benefit over a period of 6 mo in open label studies. One suggestion has been that these preparations contain small amounts of antibodies directed against monomeric and oligomeric Aβ which underlie their effectiveness in patients. To test this hypothesis, we infused Gammagard, a version of intravenous immunoglobulin (IVIG), into the lateral ventricle of amyloid precursor protein (APP) transgenic mice with pre-existing amyloid deposits. Mice were infused over 4 weeks, and tested behaviorally for the last 2 weeks of treatment. Brains were analyzed for histopathology. We found widespread distribution of human-immunoglobulin G (h-IgG) staining in the mouse forebrain, including cerebral cortices and hippocampus. Some cortical neurons appeared to concentrate the h-IgG, but we did not detect evidence of amyloid plaque labeling by h-IgG. The IVIG-treated mice had no change in phenotype compared to saline-infused animals with respect to activity, learning and memory, or amyloid deposition. APP mice infused with an anti-Aβ monoclonal antibody did show some reduction in amyloid deposits. These data do not support the argument that anti-Aβ antibodies in IVIG preparations are responsible for cognitive benefits seen with these preparations.