The extraction behavior of di-2-ethylhexyl isobutyramide (D2EHIBA) in dodecane medium for U(VI), Th(IV), and fission products such as Zr, Ce, Eu, and Cs, and the structural material Fe, has been investigated over a wide range of nitric acid concentrations. It has been observed that whereas D-U varies from < 10(-3) (pH 2.0) to 4.4 (6 M HNO3) with 1 M ligand, the corresponding D-Th values are 1.5 x 10(-3) and 4 x 10(-2). In the presence of 250 g/L of Th, D-U values are 8.6 (pH 2.0) and 2.2 (6 M HNO3). D2EHIBA has been found to be a promising extractant of trace concentrations of U in the presence of macro amounts of Th. The extraction of fission products and Fe is found to be negligible. D2EHIBA is found to extract nitric acid predominantly as a 1:1 species (K-H = 0.156 +/- 0.048). U(VI) is extracted as a disolvate UO2(NO3)(2).2D2EHIBA (K-ex = 0.87 +/- 0.08).