Objectives: This study was undertaken to find out the effects of acetylpuerarin on hippocampal neurons and intracellular free calcium in primary culture subjected to oxygen-glucose deprivation/reperfusion. Methods: According to different reperfusion time (1 h, 6 h, 12 h, 24 h), three concentrations (1.6 mu mol l(-1), 0.4 mu mol l(-1), 0.1 mu mol l(-1)) of acetylpuerarin, and MK-801 (10 mu mol l(-1)), a positive control drug, neurons were randomly divided into 21 groups. Each group was observed by inverted phase contrast microscope; neuron viability was measured by the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5diphenyltetrazolium bromide (MTT); intracellular Ca2+ was observed by Fura-2/AM ester through fluorospectrophotometer. Results: The injured neurons were protected and degeneration and necrosis were alleviated in treatment groups of acetylpuerarin and MK-801. Acetylpuerarin increased the neuron viability at high, middle and low concentrations. Fluorescence detection results showed that the calcium concentration in the group treated with acetylpuerarin and MK-801 was lowered in each reperfusion time. Conclusion: Our results demonstrated that acetylpuerarin could protect the hippocampal neurons from ischemia-reperfusion injury in rats by alleviating the morphological damage, increasing neuron viability and decreasing calcium concentration in neuron. (c) 2007 Elsevier B.V. All rights reserved.