Vanadium-base alloys, V—10% Cr, V—20% Ti, and VANSTAR-7, alloys with potential for fusion reactor application, have been irradiated in the Experimental Breeder Reactor II in the temperature range of 400 to 800°C, mainly to a fluence of 1.5 × 1022 n/cm2 (>0.1 MeV). Swelling determined both from immersion density measurements and void distribution data obtained by transmission electron microscopy showed that the V—20% Ti was completely resistant to void formation for these irradiation temperatures and for the highest fluence achieved, 6 × 1022 n/cm2. Voids formed in both the V—10% Cr and VANSTAR-7 alloys, but only the V—10% Cr, irradiated at 690 and 805° C, showed technologically significant swelling, near 1%. Swelling in this alloy at lower temperatures and in VANSTAR-7 at all temperatures was below 0.1%. Dislocation structures were complex in all three alloys. In the V—20% Ti, the scale of the dislocation network coarsened with increasing irradiation temperature. In the other two alloys, the scale of the damage, both dislocation and void components, was similar for irradiation at 496 and 580°C, but coarsened considerably to produce similar structures for irradiations at 690 and 805°C. In many cases, detail of the microstructure was obscured by strongly diffracting zones that are believed to be impurity related. Of the three alloys examined, V—20% Ti possesses the greatest swelling resistance for the irradiation temperatures and fluences achieved and thus is judged to have the greatest potential for use in fusion reactors.