This chapter discusses production of atomic defects in metals at high defect densities. Values of damage rates or displacement cross sections refer to undamaged materials. The increasing defect density during irradiation will not only influence the damaging processes e.g. by defocussing, but existing defects will also be affected by the irradiation, e.g. by recombination or changing their configuration. The cross sections for subthreshold recombination of Frenkel pairs in metals under electron irradiation with an energy E2, after damaging with electrons of energy E1, to a damage level ΔΡ are tabulated. Cross sections for recombination or transformation reactions of specific defect configurations under electron irradiation are also listed.