One of the advantages of radioisotope x-ray techniques is the potential for using primary radiation, which has enough energy to excite K x rays of even the heaviest elements. In using these penetrating x rays in the analysis, the effects of some of the most severe sources of error in x-ray techniques are less significant than when using softer L x rays. This paper theoretically illustrates the advantages of isotope-excited K x-ray determinations of heavy elements and describes some feasibility studies and applications as determination of lead in zinc and tungsten in mineral samples.