Proton transfer processes play a key role in many reactions of organic compounds and in many biochemical mechanisms. In particular, proton transfer in hydrogen bond complexes in solutions has attracted considerable attention. NMR spectroscopy is known to be a powerful tool in studying hydrogen bond and the proton transfer equilibrium. This review focuses on one specific application of this method, based isotope effect are shortly reviewed. The main subject of discussion is a relationship between the primary p DeltaH(D) on measurement of the deuterium isotope effect on chemical shifts. The factors affecting the magnitude of this and the secondary n delta13C(D),n delta15 N(D), n delta17 O(D) deuterium isotope effects and the hydrogen bond strength and symmetry, proton dynamic and position of the proton transfer equilibrium. The possibility of using the deuterium isotope effect to study proton transfer equilibrium is suggested and illustrated with representative examples of tautomeric equilibrium in beta-diketones, beta-thioketones, Schiff and Mannich bases, and proton transfer equilibrium in complexes of organic and inorganic acids with pyridine. Some experimental details of the method are given and its advantages are indicated.