Protons, electrons, and primary x rays were used to excite characteristic x radiation from individual specimens of Ti, Cr, Fe, Cu, Ge, Zr, and Au. X‐ray yield expressed as (photons /sr)/ quantum increased with quantum energy in a similar manner for protons in the range about 1 MeV and electrons in the range about 50 keV. For primary x‐ray excitation, the yield decreased with increasing quantum energy, a relationship opposite to that for proton or electron excitation. It appears that the relative values of photo‐electric absorption and scattering must be quite different for x rays and electrons to account for their opposite relationship of yield vs energy.