Void formation was studied in annealed Type 316 stainless steel irradiated with 1-MeV protons at 400 C, 500 C, and 600 C (752, 932, and 1112 F) for amounts of damage up to 50 displacements per atom (dpa). Prior to irradiation, the samples were injected with about 5 atomic ppm helium to simulate the fast-reactor situation, where helium is generated by (n,α) reactions. The volume increase at each temperature, as determined by quantitative electron microscopy, varied exponentially with displacement damage and the exponent increased with temperature. Volume increases exceeding 20 percent were associated with 50 dpa at 500 C and 20 dpa at 600 C; no limits on volume increases were apparent at any temperature. Void number density decreased and average void size increased with increasing temperature for a constant damage. A titanium-modified 316 stainless steel developed a very inhomogeneous void distribution when proton irradiated at 600 C. However, the addition of titanium did not appear to diminish the volume increase at damages between 5 and 10 dpa, when compared with ordinary Type 316 stainless steel.