The activation energies and pre-exponential factors for the self-diffusion coefficients in B2 intermetallic compounds are shown to be related to the partial molar enthalpies and entropies of the component elements. The frequently observed decreases of the activation energy and pre-exponential factor with deviations from stoichiometry are in accord with the corresponding decreases in the partial molar enthalpy and entropy. The extensive amounts of experimental data for NiAl are used to verify these relationships. It was found that the decrease of the experimentally determined activation energies for Ni in NiAl are in reasonable agreement with the decrease in partial enthalpy. The agreements between the decrease of the pre-exponential factor and partial entropy are excellent in view of the fact that the experimental values cover five orders of magnitude.