Recent preliminary data suggest that vaccination with Alzheimer's Abeta might reduce senile plaque load and stabilize cognitive decline in human Alzheimer's disease. To examine the mechanisms and consequences of anti-Abeta-antibody formation in a species more closely related to humans, rhesus monkeys (Macaca mulatta) were vaccinated with aggregated Abeta(1-42). Immunized monkeys developed anti-Abeta titers exceeding 1:1000, and their plasma Abeta levels were 5-10-fold higher than the plasma Abeta levels observed in monkeys vaccinated with aggregated amylin. These data support the use of non-human primates to model certain phenomena associated with vaccination of humans with aggregated Alzheimer's Abeta.