A five-year (1975 through 1979) retrospective analysis of all cardiac surgical patients who sustained a postoperative pulmonary embolism was undertaken, and lipoprotein profiles of these patients were evaluated. Twenty-six patients (20 men and 6 women) were identified who had definite clinical, laboratory, and radiological evidence of pulmonary embolism in the postoperative period. Twenty had undergone coronary artery bypass grafting, and the remaining 6 had undergone other cardiac surgical procedures. Of the 20 patients who had coronary bypass, 19 (95%) were found to have hyperlipoproteinemia (14 patients with type II and 5 with type IV). There were 4 hospital deaths (15%), all related to pulmonary embolism. The 4 patients had undergone coronary bypass procedures, and all had type II hyperlipoproteinemia. Since patients with hyperlipoproteinemia made up less than 10% of the coronary bypass population, the incidence of pulmonary embolism in this group is highly significant (p less than 0.001). Experimental evidence has shown that patients with hyperlipoproteinemia, especially type II, have increased platelet adhesiveness and aggregation, and coagulation abnormalities consistent with a hypercoagulable state. This retrospective study clinically confirms that finding and suggests that early postoperative anticoagulation therapy may be indicated in patients with hyperlipoproteinemia, particularly type II, to reduce thromboembolic complications.