Ponezumab (PF-04360365) is a novel humanized IgG2Δa monoclonal antibody that binds to amyloid-β (Aβ). It is designed to have reduced immune effector function compared to other passive immunotherapies for Alzheimer's disease (AD). Toxicity was evaluated in cynomolgus monkeys treated intravenously with vehicle or 10, 30, or 100 mg/kg of ponezumab every 10th day for up to 39 weeks, and after a 12-week recovery phase. The Aβ peptide sequence of monkeys is identical to that of humans. No substantial difference in test article exposure between sexes was observed, and mean plasma Cmax and AUC0-n were approximately dose-proportional. Ponezumab was detectable approximately 9 weeks after cessation of dosing. All animals, except two males given 10 mg/kg, maintained exposure to test article. One of these males tested positive for anti-ponezumab antibodies. Ponezumab was detected in the cerebrospinal fluid (CSF) of animals given active treatment. The estimated CSF/plasma ponezumab concentration ratio was <0.008 after multiple doses. At the end of the dosing and recovery phases, plasma Aβ1-40 and Aβ1-x were increased in treated animals versus controls. No test article-related effects were seen after ophthalmogical, cardiovascular, physical examinations, and clinical and anatomic pathology evaluations. Plasma concentrations of ponezumab on day 261 at the no observed adverse effect level of 100 mg/kg were 22.4 and 5.3 times greater on a Cmax and AUC basis, respectively, than human exposures at the highest dose (10 mg/kg) in a single-dose Phase I trial. These data suggest an acceptable safety profile for ponezumab as an immunotherapy for AD.