A technique for the rapid, automatic analysis of spectra from electron microanalysis of silicates and oxides with an on-line PDP- 11 of a PDP-15 computer is presented. Energy dispersive X-ray spectral data are acquired with a Si(Li) spectrometer mounted on a scanning electron microscope (SEM) or an electron microprobe and are transferred through an interface to the computer for processing. The program locates the X-ray peaks in the spectrum, determines the corresponding elements, and calculates the elemental composition of the sample. The latter computation is accomplished through the use of a linear least-squares fit of the sample (i.e., composite) spectrum with simple oxide (i. e., component) spectra. In this technique, the background continuum is not subtracted from the peak but, rather, becomes inherent in the least-squares fit.