SUMMARYPlasmodia of 10 myxomycete isolates, order Physarales, were subjected to electrophoresis in starch gel medium and subsequently stained for each of four enzymes: nonspecific esterase, malate dehydrogenase, acid phosphatase, and leucyl aryl amidase (leucine amino peptidase). The location and intensity of isozyme bands in the esterase and malate dehydrogenase patterns proved specific for each isolate tested. Bands in the amidase and acid phosphatase patterns were not specific for each isolate.Physarella oblongaandPhysarum gyrosumshared identically placed esterase bands of differing intensity. Isoenzyme patterns of esterase or malate dehydrogenase, alone or combined with other enzyme patterns, appear useful as taxonomic criteria.