X-ray instrumentation combined with a confined spot test technique has proven very useful for the determination of major constituents and trace constituents in microsamples, i.e., less than 3 mg of material. When the concentration of the major constituent is about 50%, the sample size needed is approximately 250 micron g. Samples containing as little as 0.1% of the element of interest require approximately 1 mg of sample. This technique is simple and rapid with respect to operator time and is quite versatile, being applicable to the determination of elements above atomic number 12.