This study investigated the effects of a previous sound on loudness at the absolute threshold of hearing. Change of the absolute threshold of hearing was measured when a pure tone preceded the test tone in the measurement of the threshold. The previous sound at 60 dB SPL was presented first in one ear, and then the test sound was presented in either the contralateral or ipsilateral ear at an interval of 0.5 s. When the previous sound was presented first in both ears, the test sound was presented second in one ear (left or right ear). Both the previous and test sounds had the same frequency of 500 Hz, and the same duration of 3 s. The threshold change was obtained from the difference between the thresholds with and without the previous sound. The threshold was found to be decreased by 3.1 dB when the previous sound was presented in the contralateral ear and increased by 0.9 dB in the ipsilateral ear. On the other hand, the threshold was decreased 2.3 dB when the previous sound was presented in both ears.