Unilateral occlusion effects of the nontest ears were measured from 250 Hz through 4,000 Hz in various types of hearing impairment. Bilateral conductive ears exhibited no occlusion effects at all frequencies except for 3 cases with eardrum perforation. Unilateral conductive hearing losses exhibited occlusion effects in about 30% at 250 Hz and 500 Hz, and scarcely above. Sensorineural hearing losses exhibited occlusion effects at 1,000 Hz and below in most cases. In unilateral conductive hearing losses, there was no relationship between the size of air bone gap and the size of occlusion effects. A few ears with bilateral conductive losses and unilateral sensorineural losses produced occlusion effects at 4,000 Hz also.