The microstructural modifications due to irradiation in hcp pure metals and their consequences on the mechanical properties have been investigated. Experimental results for proton-irradiated pure polycrystalline titanium are presented and discussed. Samples have been irradiated with 590 MeV protons to a low dose range at two different temperatures, room temperature and 523 K. Defect sizes and densities as a function of dose have been determined by means of transmission electron microscopy observations, and hardening has been measured from uniaxial tensile stress-strain curves. The dose dependence of the irradiation hardening has been found to depend strongly on the investigated temperatures. These results are discussed in terms of the main deformation mechanism operating at each temperature.