[General and special problems concerning the approval and re-evaluation of antimicrobial agents for use in agriculturally useful animals].

Problems associated with registration and reevaluation of drugs are discussed in this paper. In particular it deals with difficulties resulting from toleration of residue concentrations in edible tissues and from the deduction of withdrawal periods. Possible consequences when applying identical criteria for registration and reevaluation are outlined. The necessity to involve the whole veterinary profession, when setting criteria for determination, presentation and evaluation of clinical efficacy, is stressed.