Et.hylcystein dimer(ECD) was synthesized by dimerization of L-thiazo1idine-4-carboxylic acid in liquid ammania with sodium metal and successive esterification in ethanolic solution of hydrogen chlorde. The purified product was labeled with Tc in the presence of sodium glucarate(pH=5.6) and stannous chloride. Best result was obtained from the preparation consisting of O.lmg ECD, 40 ul of 0.4M sodium glucarate (pH=5.6), and 20 ug of stannous chloride. The labeling efficiency was 90% with previous condition. The labeled 99mTc-ECD was stable at least for 3 hours in PBS(pH 7.4) at roorn temperature. About. 10mCi of 99mTc-ECD was inject.ed to normal volunteer, and SPECT image of brain was obtained by triple head camera 10 minutes after inectian. The image showed similar distribution of radioact.ivity in brain with that of HMPAO image.