Exogenous pyrogens originating in the cell wall of Gram-negative bacteria have the strongest pyrogenicity (1), and for them synonyms such as endotoxins, lipopolysaccharides (LPS), and O-antigens are used. A number of attempts using affinity chromatographic approaches have been made to remove pyrogens. These are based on the specific adsorption of pyrogens, and therefore might be useful for removal of pyrogens from various solutions containing biologically active substances. One such approach is based upon the use of affinity adsorbents that contain polymyxin B as a ligand (2,3). However, polymyxin B is strongly toxic to the central nervous system and the kidneys (4) and therefore is not suitable as a ligand for removal of pyrogens from a solution, which will be used for intravenous injection. Among affinity adsorbents, immobilized histidine might be the most favorable adsorbent for removal of pyrogens because of safety, stability, and cost (5–7). Therefore, in this chapter, we describe the preparation, characteristics, and applications of immobilized histidine.