We report here on (e,2e) measurements at relativistic electron energies (up to 500 keV) under 'bound-electron Bethe ridge' conditions. Absolute triple differential cross sections for K-shell ionization of silver (E bind =25.5 keV) have been measured. Appreciable discrepancies are found with calculations in the relativistic distorted-wave Born approximation whereas results of the Coulomb-Born approximation give better accord with the experimental data. At the highest incident energy (500 keV) the Coulomb-Born approximation is in perfect agreement with the experimental results.