Results are given of a transmission electron microscope (TEM) study of the damage structure of selected alloys following ion bombardment with 46 MeV nickel ions in the Harwell variable energy cyclotron (VEC) to simulate fusion reactor exposures up to 40 dpa (̃3 MW-year m^-2) at temperatures from 475 to 650°C. The alloys were 316 L (UNS 31603), modified 316-Ti, 316-Nb, a ferritic alloy 1.4914, and the commercial alloy TENELON. The 316 L alloy is being considered for the Next European Torus (NET). At temperatures between 475 and 575°C swelling in the matrix and weld of 316 L was similar but at 625°C swelling in welds was ̃60% greater than in the 316 L matrix. The 316-Ti alloy showed only 2.5% swelling after 40 dpa at 625°C, but a maximum swelling of 10 to 14% was observed in the 316-Nb alloys. Swelling in TENELON was moderate up to 575°C but rose to 5% after 40 dpa at 625°C. Low swelling of 0.2% after 40 dpa was observed in the 1.4914 alloy. The results confirmed the superiority of the ferritic steel over the austenitic steels in respect of void-induced swelling.