It is generally agreed that etiology of chronic middle ear infection is associated with several factors involving tubal dysfunction. We studied to demonstrate the clinical findings of contralateral ear in patients with chronic middle ear infection. We analysed the local findings, mastoid pneumatization, hearing threshold and E-tube function of contralateral ears in 738 patients with chronic middle ear infection(215 cholesteatoma and 523 chronic suppurative otitis media, OMPC). Control group was 40 healthy persons. The following results were obtained : 1) Eighty-two cases(38.1%) of 215 cholesteatoma group and 234 cases(44.8%) of 523 OMPC group had normal ear drum(p>0.05). 2) Sixty-three cases(29.3%) of cholesteatoma group and 213 cases(40.7%) of OMPC group had well pneumatization(p<0.001). 3) Average hearing threshold was 26.1dB in cholesteatoma group, and 28.4dB in OMPC group(p>0.005). But in normal ear drum of the other ear in cholesteatoma group and OMPC, average hearing thresholds were 16.4dB and 19.3dB respectively. 4) The eustachian tube function was closely related with the degree of mastoid pneumatization. 5) No significant difference of local findings and pneumatization degree could be found between children and adult group(p>0.05). 6) In conclusion, the conditions of contralateral ears were similar to those of affected ears, suggesting common pathologic factors in this disorder. (Korean J Otolaryngol 37 : 6, 1994)