SINCE Armstrong and Heim1 published the original description of aero-otitis media in 1937, much has been written about this relatively new morbid process. Under the impetus of World War II and the vast increase in flying which has accompanied it, the problem of aero-otitis media has come to assume much more importance in aviation medicine than ever before. At the present moment its chief importance lies with the military in that all Army and Navy flying personnel are subject to its disabling consequences; however, the scope of the problem will widen with the advent of peace and the dawning of a new and greater era of commercial aviation. The present article is a report of observations on aero-otitis media that occurred as a result of high altitude "flights" in pressure chambers. "High altitude flights" in pressure chambers do not exactly duplicate actual flying; nevertheless the simulation of the physical conditions