Surgeons occasionally note a discrepancy between preoperative assessment of middle-ear effusion and operative observation during the placement of ventilating tubes in children's ears. This study was designed to determine whether this variance is secondary to the effects of inhalation anesthesia or misinterpretation of the preoperative exam. Observations were recorded by three distinctly different methods of measurement: the surgeon, the MD-2 Impedance Analyzer, and the Acoustic Otoscope immediately before and after induction of anesthesia. These results were then analyzed and compared with the operative findings. Anesthetic induction was shown to cause alteration in the presence of middle-ear fluid in less than 10% of cases.