Pre-and postoperative bone conduction (b. c.) thresholds were analysed in 132 ears with chronic otitis media. When the mean value of pre- and postoperative b. c. thresholds was compared, the latter was better than the former, especially in tympanoplasty type I. Significant b. c. improvement was seen for 250 to 2000Hz in tympanoplasty type I, while the postoperative b. c. thresholds were worse at 4000Hz in tympanoplasty type I, and 2000Hz and 4000Hz in modified type III. It was found that the worsening of the postoperative b. c. thresholds was mainly seen in the severe cases, followed by middle or advanced-age cases. On the contrary, improvement of thresholds had a tendency to be seen in the mild cases. The b. c. improvement is possibly due to the impedance change of the middle ear.
