Accelerator beam line components and spallation neutron targets operate in an irradiation environment where changes in mechanical properties can adversely affect component integrity. The present work presents a preliminary study of the effects of low fluences (10¹⁹ to 10²⁰ p/cm²) of 800-MeV protons on the yield strength, tensile strength, and ductility of samples of 304 stainless steel, Alloy 718, molybdenum, and tantalum. Tensile samples (0.75 or 1.6 mm thick) were directly water cooled during irradiation and were tested at room temperature. For the 304 stainless steel and annealed Alloy 718, the yield strengths increased by about a factor of 3 and 1.6, respectively, while the ductility decreased ∼30 and 40 percent. In the bee metals (tantalum and molybdenum) the yield strengths increased by at least a factor of 2. Tantalum samples retained significant ductility at room temperature, while several molybdenum specimens broke at less than 0.2 percent strain. These irradiation-induced changes at low proton fluences should not impair the usefulness of these materials (other than molybdenum) in accelerator environments.