Lectins are proteins that bind carbohydrates reversibly and are present on the membrane surface of all prokaryotic and eukaryotic cells. It is known that the carbohydrate–lectin interactions result in the initiation of a fight against or the development of a variety of conditions such as cancer metastases (1), pathological inflammation (2), and microbial infections (3). Several clinical trials approved by the United States Food and Drug Administration are under way to evaluate the use of lectins to treat a variety of infections and cancerous tumors. Because of their role in the modulation of diverse physiological processes and diseases, investigators are increasingly interested in studying lectins for the development (4) and delivery of therapeutic drugs in humans (5). Although lectin glycoarrays have been used to profile different glycoproteins (6), no agents are presently available to investigate the function of the lectin-carbohydrate complexes under in vivo conditions. In an effort to develop imaging agents for the in vivo study of lectins, de Barros et al. (7) synthesized glucose (Gl), N-acetylglucosamine (NG), and galactose (Ga) respectively conjugated to S-benzoylmercaptoacetyl triglycine (SBz-MAG3) and labeled these compounds with 99mTc to obtain [99mTc]SBz-MAG3-NG (or [99mTc]MAG3-NG), [99mTc]SBz-MAG3-Gl (or [99mTc]MAG3-Gl), and [99mTc]SBz-MAG3-Ga (or [99mTc]MAG3-Ga). The biodistribution of these radiolabeled carbohydrates was then studied in normal Swiss mice (7). This chapter describes the results obtained with [99mTc]SBz-MAG3-NG. Results obtained with [99mTc]SBz-MAG3-Gl (8) and [99mTc]SBz-MAG3-Ga (9) are presented in separate chapters in MICAD (www.micad.nih.gov).