Scaling violations and the protonneutron mass difference

We use recent electroproduction and muoproduction deep-inelastic scattering data to determine the subtraction and inelastic contributions to the protonneutron mass difference, obtained from Cottingham's formula. Adding the Born term, we predict the approximate result Mpn=1.020.66MeV. We find that the moment behaviour of the structure functions in QCD must mimic a power law form in order that the Cottingham formula converge, even though it is renormalizable in this theory.