A study has been made of the effect of 1 MeV electron irradiation on the mechanical properties of lithium fluoride single crystals tested in compression. The yield point, σ has been shown to vary with the irradiation dose, φ, according to the law σ=σu+A[1-exp (-Bφ)]1/2, where σu,AandBare constants. This relationship has been derived theoretically by considering the passage of dislocations through radiation induced obstacles dispersed in the slip plane, together with the capture of point defects by existing obstacles. The empirical relationship, σ=kφ1/3, previously used for radiation hardening in metals, is capable of representing only the medium dose results, but clearly does not fit at either low or high doses.