The technique of embryo transfer has been evaluated for the purpose of changing the mouse stocks to a germfree(GF)status.Our results showreproducible and quality-assured conversion of animalstothose which are negativeforthe presence of microorganisms.Rapid and easy access to GF mice is advantageous for studies of selected microflora andtheir cross-talks withthe host,when applying,e.g.genomic,proteomic and metabolic methodology.The studyinvolved embryotransfer in anisolator environment,thereby allowingimplantationof cleansed embryosinto GFrecipients under well-controlled conditions.The recipientfemales gave birth normally andtookcare of the offspringasif they were their own pups,thus enhancing the survival rate.Access to full technical resources required to maintain GFisolators are,however,a prerequisite.In this study,we used stainless steel isolators designed by Gustafsson(1959),on which a stereomicroscope wasmountedtofacilitate embryo transfer inside the isolator.The use of embryo transfer and isolator techniques will facilitate the availability ofvarious mouse mutant models under different gnotobiotic conditions,GF,monoxenic or polyxenic animals,to enable comparison withconventional animals for physiological and pathophysiological studies.