Nano-sized materials are now being used in medicine, biotechnology, energy, and environmental technology. Although a wide and growing number of applications for nanomaterials exist, there are limited studies available on toxicity of nanoparticles for their human risk and environmental assessment. The aim of this study was to investigate the effects of silver nanoparticles (nano-Ag) on voltage-activated sodium currents in hippocampal CA1 neurons. Nano-Ag was tested at increasing concentrations (10(-6), 5 x 10(-6), 10(-5) g/ml). The research results showed that only nano-Ag (10(-5) g/ml) reduced the amplitude of voltage-gated sodium current (I(Na)). The nano-Ag particles produced a hyperpolarizing shift in the activation-voltage curve of I(Na) and also delayed the recovery of I(Na) from inactivation. Action potential properties and the pattern of repetitive firing were examined using whole cell current-clamp recordings. Peak amplitude and overshoot of the evoked single action potential were decreased and half-width was increased in the present of the 10(-5) g/ml nano-Ag solution, and the firing rate of repetitive firing had no change. The results suggest that nano-Ag may alter the action potential of hippocampal CA1 neurons by depressing voltage-gated sodium current.