Precipitation of large ter- and quadrivalent ions by barium sulfate has been extended to the separation of uranium and the transuranium elements both from other elements and from each other. From 25 ml of solution containing sulfuric acid, potassium sulfate, and hydrogen peroxide, carrier-free quantities of barium, the light lanthanides, lead, bismuth and all the elements from radium through at least californium except uranium are precipitated to better than 99% by only 5 mg of barium ion. Polonium is also carried less completely. Uranium can be included by reducing it to the quadrivalent state with titanium trichloride either before or after precipitation of barium sulfate. Like uranium, the transuranium elements through americium can be prevented from precipitating by oxidizing them to the hexavalent state in which the oxygenated cation is too large to fit into the barium sulfate lattice. Also, because of their markedly different oxidation potentials, uranium and the first four transuranium elements can be separated efficiently from each other by proper choice of oxidant. The barium sulfate precipitate can be alpha counted directly or the radionuclides can be electrodeposited for alpha spectrometry. This procedure permits not only traditionally difficult separations such as americium from curium or the determination of extremely minute quantities of one transuranium element in the presence of large quantities of another to be made simply and quickly, but mixtures of uranium and the first four transuranium elements can be separated sequentially from each other and identified on the same sample in a single procedure. Furthermore, since virtually every alpha-emitting nuclide known can be precipitated with barium sulfate under the same conditions, chemical separation can be employed to eliminate absorbing materials and permit a true gross alpha determination in large samples.