[The sophisticated process of validation]

Current concepts on the efficient performance of validation studies are summarized. From the experience of recent attempts to validate alternative methods to animal experiments, the difficult procedure of validation should be refined. The applications of toxicological tests (safety testing) and pharmacological methods (identification of putative drugs) require different validation stategies. Suggestions as to an improved design of test development, evaluation, prevalidation, definitive validation as well as final assessment of the result are presented.