Introduction: Iranian scorpion species are classified in Buthidae and Scorpionidae with 16 genera and 25 species. In Iran, similar to other parts of the world, there are a few known species of scorpions responsible for severe envenoming. Mesobuthus eupeus is the most common species in Iran. Its venom contains several toxin fractions which can affect the ion channel. In this study purification, labeling and biological evaluation of Mesobuthus eupeus scorpion venom are described.
Methods: To separate different venom fractions, soluble venom was loaded on a chromatography column packed with sephadex G50 gel then the fractions were collected according to UV absorption at 280 nm wavelength. Toxic fraction (F3) was loaded on anionic ion exchanger resin (DEAE) and then on a cationic resins (CM). Finally toxic fraction F319 was labeled with ^99mTc and radiochemical analysis was determined by paper chromatography. The biodistribution was studied after injection into normal mice.
Results: Toxic fraction of venom was successfully obtained in purified form. Radiolabeling of venom was performed at high specific activity with radiochemical purity more than 95% which was stable for more than 4 h. Biodistribution studies in normal mice showed rapid clearance of compound from blood (2.64% ID at 4 h) and tissues except the kidneys (27%  ID at 4 h). 
Conclusion: As tissue distribution studies are very important for clinical use, results of this study suggest that ^99mTc labeling of venom can be a useful tool for in vivo studies and is an excellent approach to follow the process of biodistribution and kinetics of toxins.