For the purpose of supporting the premise that remarkable improvements in the child's attitude and performance rendered by improving the hearing impairment after aspiration of effusion and insertion of ventilating tubes in infants and children causes the increase in actual speaking time, an apparatus for measuring the time of vibration of the vocal cords was newly devised. Using this instrument, the duration of speaking time of children with otitis media with effusion was measured preoperatively and postoperatively. Preoperative and postoperative mean speaking times (speaking minutes/measured hours) were found to be 8 min 24 s per hour and 10 min per hour, respectively (number of patients: 30). These variable means were significant when examined by a Student's t-test. Pre- and postoperative speaking times showed no significant differences (10 min 24 s preoperatively and 10 min 54 s postoperatively) in the control group for surgery, consisting of 5 children having adenoidectomy and/or tonsillectomy.