Nitrites and nitrates are often responsible for methemoglobinemy. Infants, on account of their greater sensibility to oxidizing agents, are particularly liable to poison by nitrates and nitrites. Sodium nitrite can be responsible for poisoning after accidental ingestion or owing to an overdose when preparing salt provisions, or because it has been mistaken for another product. Then it is often a case of collective poisoning. Nitrates generally produce methenoglobinemy when they are changed into nitrites under the influence of a bacterial proliferation or of a reductase held in plants. It happens with spinach and carrot soup. Nitrates can pollute municipal water supply and chiefly well water. As regards therapy, cases of methemoglobinemy have been noted after an overdose of potassium nitrate and especially of bismuth subnitrate. The treatment of methemoglobinemy caused by nitrates and nitrites is not specific: suppression of the oxidizing agents, oxygenation, prescription of reducing agents.