In order to overcome particle-size and sample inhomogeneity effects in the analysis of environmental samples by energy-dispersive x-ray spectrometry, an automated borate fusion procedure was investigated and applied to the analysis of NBS-SRM 1633 Fly Ash and NBS-SRM 1648 Particulate Matter. Twelve elements in each sample were determined and the results are in agreement with NBS certified values and/or those of other workers, usually within ± 5 to 10per thousand for most elements over the concentration range from 70 ppm to 15per thousand. Fly Ash samples were fused with the heavy absorbers La2O3 or WO3 and analyzed using a linear calibration curve, assuming no matrix effects. The particulate samples, however, were fused with lithium tetraborate only and the data were corrected for x-ray absorption and K x-ray line interfaces by a NBS mathematical procedure. The limits of detection of this procedure for most of the elements analyzed in the sample were between 10 to 100 ppm.