The degradation of polyethylene and polyoxymethylene crystals in the high voltage electron microscope was determined from 100–1000 kV. As in previous work at lower electron energies, the dose needed to change the initial crystalline diffraction patterns into amorphous ring patterns was measured. It was found that the dose required to destroy the crystal order increases by a factor of about three in going from 100 to 1000 kV. The result agrees roughly with the theoretically predicted ionization rate, assuming that the damage rate is proportional to the ionization rate.