Both electron and proton induced x-rays can be used for analytical purposes. We have compared their relative sensitivities for detecting various constituents in a well characterized NBS low alloy steel standard. Both energy dispersive and wavelength dispersive spectrometry were used in detection, and optimum beam energies were used in excitation. We find that for an equal accumulated charge the detection sensitivity by proton induced x-rays was a factor of two to three times greater than by electron induced x-rays for all elements. The increase in x-ray production by using proton energies above the level available to us (3 MeV) is rarely warranted in view of a corresponding increase of x-ray absorption losses in the target. © 1977, American Chemical Society. All rights reserved.