For the development of Tc-99m-labelled antimony sulfide colloid and hydroxyethyl starch, various experiments such as preparation of colloid, control of the distribution of particle size, establishment of labelling conditions, determination of labelling yield and radiochemical purity, examination of stability, and organ imagings of rabbits etc. were carried out. 1) Antimony sulfide colloid was readily prepared by the reaction of aqueous solution of antimony potassium tartrate with hydrogen sulfide generated by treating ferrous sulfide with dilute sulfuric acid. The colloid could be stabilized by adding small amount of polyvinylpyrrolidone. 2) Electron microscopy analysis exhibited the distribution of colloid size in the range of 1∼15 nm with a major portion of 9 nm. The colloid solution was sterilized by membrane filtration (0.2 μm) and then stored at 4℃. This sterilized colloid was so stable that it was usable at least for one year. 3) The antimony sulfide colloid was labelled by adding sodium pertechnetate-Tc-99m solution to the reaction vial, followed by adding hydrochloric acid and then boiled for 30 min. The optimal pH of the reaction mixture was found to be in the range of 1.3∼1.4. Instant thin layer chromatography (ITLC) analysis showed high labelling yield of above 99.5%. This labelled colloid maintained high radiochemical purity of above 99% until 10 hours after labelling. 4) Animal studies showed high uptake of Tc-99m-Sb2S3 colloid at lymph vessels and nodes indicating a suitable agent for lymphoscintigraphy. Satisfactory results were also abtained in other clinical studies. 5) Hydroxyethyl starch (HES 0.6∼1.0%) was labelled with Na99mTO4, in the presence of SnCl2 with high labelling yield of above 99.5%. The optimal pH of the reaction mixture was in the range of 1.8∼2.0. Tc-99m-HES maintained high radiochemical purity of above 99% until 10 hours after labelling. 6) Animal studies showed that Tc-99m-HES migrated more rapidly from the injection sites into the lymph vessels than Tc-99m-Sb2S3 colloid while less amount of the former was uptaken at lymph nodes than that of the latter. Similar phenomenon was also observed in other clinical studies. As a result, Tc- 99m-Sb2S3 colloid was found to be more effective lymphoscintigraphic agent than Tc-99m-HES.