This chapter discusses on production of atomic defects in predamaged metals. The production of defects under irradiation can be influenced by the presence of lattice defects. These can be introduced by quenching (vacancies, vacancy clusters), by plastic deformation (vacancies, dislocations) or by previous irradiation (interstitials, vacancies, clusters). Subsequent heat treatment allows to modify the defect structure (partial annealing, clustering) prior to irradiation. The introduction of vacancies in metals by quenching has no effect on the low temperature damage rates of aluminum (Al) and gold (Au) under neutron irradiation. In platinum (Pt), an increase of the initial damage rates by about 10% was observed under electron, deuteron and fast neutron irradiation. At higher doses, a slight decrease was found in quenched Pt. Deformation at room temperature enhances the damage rates under neutron irradiation. The damage rates of deformed and undeformed Al, Au and Pt under 20 MeV deuteron irradiation at 6 and 8 K are compared. In platinum, measurable enhancement of damage rate in deformed specimens was only observed after aging. Damage rates in preirradiated metals are reduced in comparison to damage rates in virgin material. This is due to recombination of existing Frenkel pairs by energy transfers by the irradiation particles (so-called subthreshold events) and by recombination of newly formed interstitials with existing vacancies or vice versa (so-called spontaneous recombination).