Proper use of terminology and classification of various categories of effusion throughout the world is necessary if we are to obtain dissemination of pertinent scientific and clinical information and to make progress in understanding and eradicating this widespread group of diseases. The general term, middle ear effusion, and the categories serous, mucoid, and purulent are suggested to describe collections of fluid in the middle ear; the use of other descriptive terms should be influenced by the nature of the clinical, cytologic, bacteriologic, histopathologic and chemical findings in the fluid and lining membrane of the middle ear.