This is the report of the thirty-third of aseries of workshops organised by the Euro-pean Centre for the Validation of AlternativeMethods (ECVAM). ECVAM™s main goal, asdefined in 1993 by its Scientific AdvisoryCommittee, is to promote the scientific andregulatory acceptance of alternative methodswhich are of importance to the biosciencesand which reduce, refine or replace the use oflaboratory animals. One of the first prioritiesset by ECVAM was the implementation ofprocedures which would enable it to becomewell-informed about the state-of-the-art ofnon-animal test development and validation,and the potential for the possible incorpora-tion of alternative tests into regulatory pro-cedures. It was decided that this would bebest achieved by the organisation of ECVAMworkshops on specific topics, at which smallgroups of invited experts would review thecurrent status of various types of