A new nondestructive technique has been developed to permit the assay of uranium in nuclear material that is "infinitely-thick" with respect to the 185.7-keV gamma ray. This new method not only provides a way of analyzing material that previously could not be analyzed, but also removes the requirement for geometry and self-absorption corrections. Assays, in g U/g, are determined using the ratio of the 98.4-keV uranium X rays generated from fluorescence activity to the 185.7-keV gamma ray from 235U. Enrichment values needed for the assay calculation can be nondestructively determined from the same spectrum if they are not known. The weight of the sample can then be used to obtain absolute quantities. In material containing large amounts of uranium the mass absorption coefficients for the 235U gamma ray and uranium X ray are nearly the same. Thus, no self absorption corrections are necessary. A number of different uranium materials in a variety of configurations were analyzed with an average difference of 6% between accepted and measured results.