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Sixteen subjects read intelligibility tests while waring headphones. Each subject read four tests, one at each of four levels of intensity of the side-tone in his headphones. A constant level of background noise was in the headphones, only the amplification of the speaker-induced signal varying. A panel of listeners heard the recordings, in a noise-filled room (110-114 db) in the manner of an intelligibility test. Also through the tracings of a graphic level recorder the intensity of the speaker's readings of the test items was measured. Analysis showed that speaker increased in vocal intensity with diminished side-tones, and that intelligibility scores likewise increased when the speaker heard less intense side-tones. (Author)