ABSTRACTDidymium iridismyxamoebae and Plasmodia were cultivated in liquid peptone-glucose-yeast media or on plain agar withEscherichia colikilled by mild heat treatment. Fifteen of sixteen heterothallic strains could be maintained by serial transfer on the axenic medium. There was no difference in mating and sporulation frequency between never axenized strains and axenic strains reassociated with live bacteria at the time of mating. Axenic strains mated under axenic conditions formed plasmodia at the same frequency as the above crosses but the sporulation frequency was reduced by one-half.