L- Histidine is a very important amino acid and is widely distributed in living systems. In the growth and multiplication of animal cells, it was found that L-histidine is one of the amino acids that must be present. From the kinetic studies of certain enzymes such as chymotrypsin and ribonuclease, it has been proposed that the imidazolyl group of the histidine residue may serve as the basic electron donor, and that the histidine residue in some cases may be the active site of the enzyme. The interactions of L-histidine with heavy metal ions, including Ni (II) (1), Zn (II) (1, 2), Fe (II) (1), Cu (II) (3, 4, 5, 7, 9, 10), Mn (II) (6), Cd (II) (3, 4) and Co (II) (1, 11, 12), have been investigated.