Haemoglobin is a globular protein, functions in transport of oxygen, carbon dioxide and protons. It also acts as intracellular buffer thus involved in acid base balance. Haemoglobin consists of four polypeptide chains, each with a haem group with a central iron. Adult haemoglobin (α2β2) is a tetramer of two subunits type 2α and 2β. The oxygen binding curve of haemoglobin is sigmoidal, which indicates that the binding of oxygen to haemoglobin is co-operative. The regulation of oxygen binding by hydrogen ions and carbon dioxide is called the Bohr effect. The affinity of haemoglobin for oxygen is further regulated by 2, 3-bisphosphoglycerate (2, 3-BPG). Haemoglobinopathy is the mutation in the genes that code for α and β chains and can affect the biologic function of haemoglobin, e.g. sickle haemoglobin, thalassemia, etc. Haemoglobin derivatives can be grouped into normal and abnormal derivatives. Oxyhaemoglobin, reduced haemoglobin and carbaminohemoglobin are normal haemoglobin derivatives, while methaemoglobin and carboxyhemoglobin are the abnormal haemoglobin derivatives.