AbstractThe relative sensitivity of an analytical electron microscope and energy‐dispersive x‐ray detector to x‐rays of various elements is investigated through an extensivekASifactor study. Elemental standards, primarily National Bureau of Standards multielement research glasses, were dry‐ground into submicrometer‐sized particles and analyzed at 200 kV accelerating potential. The effect of self‐absorption of x‐rays by the particle has been corrected for, allowing the experimentalkASifactors from this study to approximate those that could be obtained from “infinitely thin” specimens.Whenever possible, elementalk‐factors were determined by the analysis of many (up to a maximum of nine) different standard materials. ExperimentalkASifactors were calculated for a wide range of Kα, Lα, and Mαx‐ray lines. For comparison, theoreticalkASifactors, employing a variety of ionization cross sections, were computed. Good agreement is obtained between several of the theoretical k‐factor models and the experimental results. Mass volatilization of Na and K from the small glass particles during analysis is discussed, as are observations that the grinding and/or dispersing of standard materials in a liquid (such as ethanol) may promote leaching of certain element