The investigation of hearing by the use of a fatiguing tone and an immediately subsequent short-duration test tone, first used with good success by de Maré and later adapted for special problems by Lüscher and Zwislocki, Gardner, and Munson and Gardner opens a wide field for study of suprathreshold events in the ear. Among the many variables are the frequency, intensity, and duration of each of the two tones, the frequency relations between the two tones, and the recovery interval, if any, between them. Most of these variables have not been studied independently. The present paper explores fatigue as a function of (1) duration and intensity of the fatiguing tone, and (2) duration of recovery interval. Both variables will be considered with respect to the frequency of the fatiguing tone.