Abstract The redox and associated chemical behaviour of ε-adenine, ε-adenosine and ε-NAD + and their reduction products in buffered aqueous media have been examined by electrochemical, photochemical and spectroscopic techniques. In the pH range 1–8, ε-adenine and ε-adenosine undergo similar two-electron reductions in the pyrimidine ring, with formation of an unstable reduction product. Reduction of the 2,3 double bond of the pyrimidine ring is suggested. ε-NAD + gives rise to two polarographic waves in the pH range 2–12, but the mechanisms in acidic and alkaline media are different. The mechanism of reduction of NAD + in neutral and alkaline solutions involves two one-electron reduction steps of the nicotinamide ring, as for NAD +. However, in acidic medium the first one-electron reduction of the nicotinamide ring is followed by reduction of the ε-adenine moiety of the ε-NAD + molecule. The photochemical transformations of the reduction products upon U.V. irradiation have also been examined.