Abstract: The paper describes the preparation of ~(99)Tc~m-CPI for clinical evaluation.~(99)Tc~m--CPI (~(99)Tc~m--2--Methyl--2--Isocyano-- Propionate) was synthesized, usingthe improved stannous chloride reducing method. The effects of pH, reacting time,Sn~(2+) and GH concentrations were studied. The optimum conditions for ~(99)Tc~m--CPIlabelling are: pH 5.0～7.5, SnCl_2 concentration 0.15～0.50 mg/ml and GH 2～50mg/ml. The labelling efficiency is(93.6±1.47)%. The biodistribution in guineapigs is observed and excellent myocardial localization has been found in dog. Wesuggest that the ~(99)Tc~m--CPI prepared with these labelling conditions may be used inclinical trial for myocardial imaging.