The author suggests the following problems toward the solution of which important contributions might be expected by employing the technique developed by him for freeing termites from protozoans by oxygenation: (1) Elimination of Nosema from silkworms and other insects; (2) elimination of protozoan parasites from fish, particularly in hatcheries; (3) freeing of plants and insect carriers of protozoans in diseases caused by flagellates, and in other diseases in which some connection with protozoa has been suspected; (4) immunization, using oxygen to produce attenuation; (5) sterilization of culture media. Several problems of general biological importance touching on the relation of microorganisms to their animal and plant hosts are proposed for study by this method.