Methaemoglobin (metHb) is a form of protein haemoglobin in which iron is present in the form of Fe3+ instead of normal Fe2+ state. MetHb fail to bind oxygen with it. This causes oxygen deficiency in the tissues as they can’t get the oxygen and functional anaemia as well. If the metHb level in the blood is 1-2%, it is normal and one need not to worry about it. Generally, inorganic and organic nitrates and nitrites, aromatic amines and other toxic industrial chemicals make metHb by binding with Hb instead of O2. Apart from these, at times chromates, chlorobenzene, fertilisers and herbicides also bind with Hb to form metHb. In case of metHb reductase deficiency and G6PD (glucose-6-phosphate dehydrogenase) deficiency, the level of metHb rises in the blood.