Vanadium and other group V metals and alloys exhibit much higher hydrogen permeabilities than palladium alloys, and the basis of this lies primarily in their high hydrogen solubility. Because absorbed hydrogen profoundly influences the physical and chemical properties of the host metal, classical absorption and diffusion theories, which assume low concentrations of solute, may not apply to these alloys. To elucidate hydrogen transport through nondilute alloy membranes, a comprehensive series of absorption and flux measurements have been made for three V–Ni alloys over a range of pressures and temperatures. Alloy disks of three compositions (V95Ni5, V90Ni10, and V85Ni15 atom %) were sectioned from arc-melted ingots and coated on each side with a Pd dissociation catalyst. Hydrogen absorption and desorption isotherms were calculated using the Sieverts’ method, and hydrogen flux was measured using the constant-pressure permeation method. The pressure–concentration relationships of these alloys were nonideal, particularly at high hydrogen concentrations. As a result, the diffusion coefficients for each alloy exhibited a significant hydrogen concentration dependence, which illustrates the nonapplicability of Fick’s first law of diffusion to these alloys. A strong dependence on Ni content was also observed. During permeation the hydrogen concentration gradient increases with increasing distance from the feed surface.