Isoenzymes of phosphoglucomutase and hexokinase were repeatedly evaluated using starch gel electrophoresis in polyxenic cultures of Entamoeba histolytica. In two out of 18 strains spontaneous changes of isoenzyme patterns were recorded. While originally they were categorized into virulent group of zymodemes, following isoenzyme analysis classified them as non-virulent. The relation between virulence and isoenzyme pattern is questionable.