The purpose of this study was to investigate the dynamics of nickel contained in shape memory alloy implants （SMI）．An SMI removed from a patient 4 years after placement was studied by X-ray photoelectron spectroscopy．The conclusions were as follows：
　1．Oxygen，titanium，carbon，and nitrogen were detected on the implant surface；no nickel was detected．
　2．The titanium on the implant surface was present as TiO₂． A small amount of Ti（OH）₂ was also detected．
　3．The metal peak of titanium was first detected at a depth of 4 nm and that of nickel was detected at a depth of 0.67 nm．
　4． At a depth of 0.67 nm from the implant surface，nickel was present as NiO and metal．Titanium was present as TiO₂, TiO_X，and TiO．
　The results of this study did not allow us to determine whether nickel was not initially present on the implant surface or it had undergone elution in the body．Studies are urgently needed to clarify this point．