Using special procedures, we investigated monaural spatial sound as perceived in the horizontal plane in 30 otologically healthy subjects, aged 17 to 23 years. It was found that on the masked side (over 50 dB) the localization of sound sources in this plane was disturbed and the numbers of loudspeakers as indicated by the test subjects were shifted towards the open ear. On the open side they showed the ability to locate a loudspeaker positioned at an angle of 18 degrees and failure to locate loudspeakers positioned at angles of 9 degrees and 27 degrees. Also, 60 audiologically healthy people in the age group from 21 to 70 years were examined. Most subjects displayed a similar pattern of response which seems to be independent of their age, sex or the state of concha auriculae.