(A fee may be required to access this article.)  Samples of siliceous solids up to 1 g were dissolved completely by successive fusions with potassium fluoride and pyrosulfate in platinum dishes in the presence of appropriate tracers. Samples which contaminate or react deleteriously with platinum were treated extensively with hydrofluoric and perchloric acids before fusion with pyrosulfate in glass. The pyrosulfate cake was dissolved in dilute hydrochloric acid and the actinides were precipitated isomorphously with barium sulfate. The barium sulfate was dissolved in alkaline ethylenediaminetetraacetic acid (EDTA), and the actinides were precipitated as the hydroxides, filtered on a membrane filter and analyzed in an alpha spectrometer. When necessary, the hydroxides were converted to fluorides in the presence of various oxidizing agents to obtain improved resolution and additional separations. Isotopes of all elements from thorium through curium can be determined in one sequential procedure. The procedure was simpler and faster than others available, with higher yields and greater reliability. Resolution of the subsequent alpha spectra was comparable to that obtained by electrodeposition. The results were reproduced with a relative standard deviation of 1 to 2%. The accuracy of the determination on standards was generally as good as the statistical uncertainty of the measurement permits. Some results of actinides in pond sediments, incinerator ash, baghouse dusts, and ion exchange resins are given.