A comparative study has been carried out on the effect of Sn(II) tartrate and Sn(II)Cl2on the labelling efficiency and tissue distribution of99mTc-human serum albumin. The effect of reductant content, reaction time (incubation time), albumin content, pH, and ascorbic acid on the efficiency of labelling and the tissue distribution of the labelled albumin has been investigated. The percent labelling was determined by paper and thin layer radiochromatography. Ascorbic acid shows no effect on either labelling efficiency or tissue distribution of99mTc-HSA prepared by Sn(II) tartrate or Sn(II)Cl2.