Rare‐earth screens (Rarex types B and BG) were calibrated against Kodak No‐Screen x‐ray film using pulsed x radiation. Type B screen, which contains only an yttrium compound, is over 50 times more sensitive than No‐Screen film in the energy range above 17 keV and is the preferred screen, of the two tested, in the energy range below 50 keV. Type BG screen, which contains yttrium and gadolinium compounds, is 1.5 times less sensitive than type B below 50 keV (the Gd absorption edge) but 3.5 times more sensitive above 50 keV. All of the calibrations were accomplished with monochromatic x rays from secondary fluorescers. The results should be accurate for pulses of shorter duration than 1 msec, which is the decay time of the screens.