At present, X-ray fluorescence and electron probe analysis are suitable for all atomic numbers down to 11 (Na). Precision for major constituents is about 1 per cent of the amount present for X-ray fluorescence but 3 to 5 per cent for electron probe analysis because of the relatively higher background. The limit of detectability is about 1 ppm or 10⁻⁸ g for X-ray fluorescence and about 100 ppm or 10⁻¹⁴ g for the electron probe. A number of improvements are likely in the near future that will extend the present limit considerably. These include: (1) measurement of the elements from boron to fluorine, (2) specimen pretreatment by techniques especially designed for X-ray analysis rather than wet chemistry, (3) selective excitation and detection of X-rays from only a few desired elements in a complex specimen, and (4) use of high-speed computers with suitably designed mathematics to eliminate the requirement for known comparison standards in quantitative analysis.