Perstimulatory loudness adaptation was measured by two techniques which utilized varying amounts of simultaneous contralateral stimulation. In the first experiment a single‐SDLB (simultaneous dichotic loudness balance) method was employed with comparison signals of 200‐ and 2000‐msec duration and with an adapting signal of 8 sec. More adaptation was noted when the longer comparison signal was employed. In the second experiment, a modified tracking procedure utilized comparison signal duty cycles of1623%and 50%. The higher duty cycle yielded a greater magnitude of test‐ear adaptation than did the lower duty cycle. The results support the hypothesis that perstimulatory loudness adaptation is dependent on simultaneous binaural stimulation and, in addition, is related to the amount of that stimulation. It is therefore concluded that adaptation is not a monaural or a purely peripheral phenomenon.