Despite prophylactic therapy, pulmonary embolism remains the leading cause of perioperative mortality in patients undergoing total knee arthroplasty (TKA). We used transoesophageal echocardiography to monitor 29 consecutive patients during TKA. Showers of substantial amounts of echogenic material, lasting for 3-15 min, were visible in the right atrium and ventricle within 10-15 s of tourniquet deflation in all patients. A 3 x 6 mm fresh thrombus was aspirated from the central circulation of one patient. Another patient, who had had a Greenfield filter placed for previous thromboembolism, showed very little echogenic material after tourniquet deflation. The composition and importance of these echogenic emboli remain uncertain.