Abstract Relative secondary ion yields of 12 metals and 2 semiconductors have been determined under ultrahigh vacuum conditions as a function of the primary argon ion energy between 2 and 15 keV. The ion yields were found to exhibit a strong energy dependence which cannot be accounted for by the energy dependence of the sputtering yield. Very pronounced effects are found with elements for which kinetic ionization is important. The relative secondary ion yields vary by less than two orders of magnitude, aluminium showing the largest and gold the smallest yield. Above about 10 keV the results can be described to within a factor of two by a recently developed ionization model if reasonable assumptions are made with respect to the physical parameters of the bombarded surface.