An instant kit of cysteine (amino acid) to be labelled with99mTc was prepared. Optimal conditions were found, and a procedure to prepare the kit ready to use in liophilized form to gain the highest labelling yield. More than 95% labelling yield was obtained when99mTc (TcO
) eluted from99mTc-generator was added to the contents of the kit. Each kit contains 0.66 mg of SnCl2·2H2O as stannite and 66 mg cysteine in lyophilized form. The formulation of cysteine tin (kit) was stable for nearly three months giving labelling yield more than 95%. Using GCS technique, different species of technetium and labelled cysteine were identified when Sephadex (G-50, G-25) was applied. Biodistribution of the labelled preparation revealed that kidney was the target organ. The ratio of accumulated dose in kidneys/liver was greater than 2.