Patch clamp is a useful method to study ion channels in cell membrane. By means of repatched whole cell, it becomes available to monitor the long term effect of some kinds of reagents on ion currents of a single cell without wash-out problem. After the cell was whole cell patched, drugs can be conveniently dialyzed into the cell from the pipette. The neurotoxicity of MPP⁺ in dopaminergic neuronal cell line (MN9D) was investigated with repatched whole-cell method. It was found that the voltage dependent calcium current (I_Ca) was significantly suppressed in differentiated cells and I_Ca induced by high depolarizing pulse decreased earlier than that induced by low depolarizing pulse during MPP⁺ treating for up to 1 h. In undifferentiated cells, no apparent change happened under the same condition.