The incidence of severe hearing loss after coronary artery bypass graft surgery has been as rare as 1/1000 surgery (Plasse et al., 1981). To evaluate possible changes in the auditory status, audiograms were taken before and after this operation. Our objectives were to: 1) evaluate hearing losses that were not necessarily severe and 2) examine the factors associated with any auditory insult. we selected patients among a group without any history of hearing problems and the intake of any ototoxic drugs. All patients underwent careful examination and hearing evaluation the day prior to surgery. 6 days after surgery they were examined again and asked about any hearing problems or experience of tinnitus. Various operative details were taken and the post-operative drug record examined. Patients who were too ill for retesting, or who had been given sedative or ototoxic drugs or opiate analgesia, were dropped from the study. The whole procedure was repeated on a control group of 20 patients who were having thorocotomy but without being placed on a cardiopulmonary bypass. From the bypass sample of 40 ears, five of them (four individuals) had an individually statistically significant high-frequency hearing loss. The results showed a statistically significant difference between the bypass group and the control group, with the bypass patients having worse threshold shifts following the operation.Discriminant analyses have shown that those patients suffering hearing impairment may be discriminated principally with four variables: the patient's age, minimum temperature and minimum blood pressure during the operation, and the time on bypass.