Free purines are found in some of the biological Systems. Some types of purines as consti- tuents of large molecules however are found in every living celi. Uric acid is a purine derivative which was discovered över one hundred years ago. It is found in blood, cerebral spinal fluid and milk. Bird excrement, guano contains a significant amount of uric acid. Uric acid as well as other oxypurines are the majör products of purine metabolism in man. Presence of adenine and guanine in nucleic acids is important in transfer of genetic infor- mation. Oxidation and reduction of purine derivatives in human and animal metabolisms have been studied extensively. Electron transfer mechanisms of purines, are therefore important in stud- ying their role in biological Systems. In the present study the electron transfer mechanisms of some biologically active purines are discussed.