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, followed by the presentation of the test sound in either the contralateral or ipsilateral ear at an interval of 0.5 s. Both the previous and test sounds had the same frequency of 500 Hz, and the same duration of 3 s. The change of the threshold was obtained from the difference between the thresholds with and without the previous sound. The threshold was found to be decreased significantly by approximately 2 dB when the previous sound was presented in the contralateral ear. On the other hand, the threshold was only slightly changed when the previous sound was presented in the ipsilateral ear. These experiment results suggest that loudness was increased by perceiving the previous sound in the contralateral ear.