Nanosilver has been widely used in medical biology; however, the distribution and interaction of nanosilver with cells is still unclear. There have been some reports demonstrating that nanoparticles can cross the blood-brain barrier (BBB). The present study investigated the accumulation of silver nanoparticles in the brain, and the effects of silver nanoparticles on BBB. Nanosilver and microsilver (62.8 mg/kg) particles were subcutaneously injected into rats. The rats were sacrificed at predetermined time points and the brains were obtained for ultrastructural observation and silver level detection. The results showed that silver nanoparticles could traverse the BBB and move into the brain in the form of particle. The silver nanoparticles can induce neuronal degeneration and necrosis by accumulating in the brain over a long period of time. (C) 2008 Elsevier B.V. All rights reserved.