Abstract: HL91 kit in lyophilized form is obtained by freeze-drying in the presence of stannous tar-trate as reductive agent, and labelled with 99Tcm. The optimal labelling condition is determined by pH and the content of stannous tartrate. Under the condition of pH7~9, 1 mg HL-91,5~30μg stannous tartrate, the labelling yield is above 90%. Every kit formulation contains 1 mg HL91, 20 μg stannous tartrate,pH8~8. 5. The kit is eligible according to acute toxicity,asepsis and pyrogen-free examinations. The labelled complex is stable in about 5 h at room temperature. Stability studies show that freeze-dried formulations stored at room temperature for 1 month and in refrigeratory from 3 to 6 months, the radiochemical purity are still above 90%.