A strongly alkaline base, NH2.CNH.NH2, formed by the oxidation of guanin, and also obtained combined with methyl in the decomposition of creatin. Boiled with dilute sulphuric acid, it yields urea and ammonia.

Guanidine is a crystalline compound of strong alkalinity formed by the oxidation of guanine. It is used in the manufacture of plastics and explosives. It is found in urine as a normal product of protein metabolism.