Abstract: Objective To observe the interaction between Cd and Se on Ca²⁺i and pro tein kinase activity in neurons.Methods We detected the activity of Ca²⁺i and protein kinase(PKA,PKC)in isolated neurons in different conditions.Results The result shows that the Cd dose of 5~50 mol/L decreases intracellular free Ca²⁺ concentration(Ca²⁺i)and PKA activity,and increases PKC activity,however the Cd dose of 500 mol/L increases significantly Ca²⁺i in nerve cell,and PKA,PKC activity.The Se dose of 5 mol/L does not cause the variation of Ca²⁺i in nerve cell,and has no effect on the variation of intracellular free Ca²⁺ concentration caused by Cd in neurons.Conclusion The present study shows that study in vitro is not suitable for the study that Se inhibits Cd toxicity.