Histidine (His;H) is an essential amino acid and is required for the synthesis of various substances, including histamine, glutamate and haemoglobin. it is vital for the O2 carrying capacity of hemoglobin and their by ensures indirectly the oxygen supply to all the organs and tissues. It ensures sufficient energy supply in the cells and can detoxify the body of heavy metals through its ability to combine with them. Nutritional supplements containing L-histidine are very helpful during the recovery process after an operation or injury.