The thermodynamics of six reactions of nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate is discussed both from the viewpoint of the chemical equations and the biochemical equations for these reactions. Tables of the standard enthalpies of formation and standard Gibbs energies of formation of species are presented and are used to calculate standard enthalpies of reaction, standard Gibbs energies of reaction, and equilibrium constants K of chemical reactions at 25 degrees C, 1 bar, and ionic strengths of 0, 0.1, and 0.25 M. These tables are used to calculate standard transformed enthalpies of formation and standard transformed Gibbs energies of formation of reactants, standard transformed enthalpies of reaction, standard transformed Gibbs energies of reaction, and apparent equilibrium constants K' of biochemical reactions at 25 degrees C, 1 bar, pH 7, and ionic strengths of 0, 0.1, and 0.25 M. Since these reactions do not involve pK's of acid groups in the vicinity of pH 7, these reactions produce exactly 0, 1, or 2 mol of H+ per mole of reaction. The calculations are compared with experimental values.