Selected substances have been examined by X-ray fluorescence to determine the effect of particles or surface irregularities on the fluorescent intensity. The powdered substances examined were segregated into particle size classifications by the use of standard and micro sieves and ocular microscopic measurements. The substances thus classified were Iron, germanium, and titanium metals, copper furnace slag, and a cobalt molybdate catalyst. Graphical representations are used to characterize the relation between particle size and intensity. In certain cases the influence of particle size is expressed in terms of a calculated absorption length of the substance. The extent to which particle size in a powder affects the fluorescent intensity is a function of the absorption coefficients of the substance for the exciting and fluorescent X-rays, The effect on intensity of successive powder dilution of a high atomic number witha low atomic number substance has been measured. The results are of assistance in providing a concept of the structure necessary for maximum intensity. Little difference in the fluorescent intensity of an element is exhibited as between its dilution in a dry powder and in an aqueous solution, if the absorption properties of the two diluents are very similar. The effect of small surface irregularities in a metal exhibits no systematic relation to the fluorescent intensity.