Pure nickel, a “pure” Type 316 stainless steel (P7), and two high-strength copper alloys have been irradiated with either 14-Me V nickel or copper ions to a peak damage level of 50 displacements per atom (dpa) (K = 0.8) at homologous temperatures ranging from 0.4 to 0.6 Tm. The irradiated foils have been examined in cross section in an electron microscope. The injected interstitial effect on the suppression of the measured void densities in nickel and P7 was found to increase with decreasing temperature. The comparison of these results with nucleation theory shows good qualitative agreement. Quantitative discrepancies are attributed to diffusional spreading of point defects and to the presence of impurity atoms in the matrix. A copper alloy irradiated at 300°C showed a small heterogeneous void density characteristic of the high temperature end of the void swelling regime, while no voids formed in the alloys irradiated ≧400°C. This result is in excellent agreement with nucleation theory that indicates the void swelling regime in ion-irradiated, low impurity copper should be less than 300°C (0.42 Tm.