The ability to make therapeutic decisions regarding excessive fibrinolysis in the perioperative period is limited by the lack of availability of a near site monitor of fibrinolysis. We investigated the use of a latex agglutination D-dimer assay to detect perioperative fibrinolysis in patients undergoing thoracic surgery with and without extracorporeal circulation. We studied 27 patients who underwent thoracic surgery requiring cardiopulmonary bypass (CPB; coronary artery bypass grafting, n = 12; valvular surgery, n = 15) and a cohort of 20 patients who underwent noncardiac thoracic surgical procedures not requiring CPB. The purpose of this investigation was to determine the relationship among alterations in the latex agglutination D-dimer assay, use of extracorporeal circulation, type of cardiac surgical procedure, and mediastinal and/or chest tube drainage (cardiac surgery only) in patients undergoing thoracic surgery. Perioperative D-dimer levels, measured by latex agglutination, had significant (P < or = 0.05) intragroup changes among patients undergoing cardiac surgery (requiring CPB) and the cohort of patients who underwent noncardiac thoracic surgery without CPB. Although intraoperative D-dimer levels were not increased in patients undergoing noncardiac thoracic surgery, postoperative levels were significantly (P < 0.05) increased (compared with preinduction). In cardiac surgery patients requiring CPB, intraoperative D-dimer formation was significantly (P < or = 0.05) increased but did not demonstrate any intragroup (coronary artery bypass grafting versus valvular surgery) differences. Finally, D-dimer levels were not associated with postoperative mediastinal and/or chest tube accumulative drainage measured at intervals up to 48 h postoperatively in patients undergoing cardiac surgery requiring CPB. Our study indicates that the latex agglutination D-dimer assay can detect excessive fibrinolysis perioperatively, and that extracorporeal circulation can significantly influence the pattern of D-dimer formation in patients undergoing thoracic surgery. We assessed the ability of a readily available D-dimer assay to detect excessive fibrinolysis in patients undergoing thoracic surgery with and without extracorporeal circulation. The findings demonstrate that the assay used in this investigation reflected variable amounts of fibrinolysis in patients undergoing both types of thoracic surgery.