Two natural semiconducting diamonds were pre-heated at 13SO°C, irradiated at 77°K with approximately 2 × 1016electrons/cm2at an energy of 1 MeV and heated for successively increasing periods of time at temperatures in the range 200 to 1200°C. The annealing of the irradiation damage exhibits at least three direct stages and one reverse stage. Direct and reverse annealing are defined as producing changes, respectively, in the opposite direction to, and in the same direction as, those produced by the irradiation damage.