['To determine if the platelet glass bead retention assay can predict bleeding after cardiac surgery.', 'Prospective, observational study.', 'Large, tertiary care, academic medical center.', 'Forty-three adult patients scheduled to undergo elective cardiac surgery employing cardiopulmonary bypass (CPB).', 'Whole blood samples were observed for platelet count, prothrombin time, and platelet (glass bead) retention assay. The platelet retention and prothrombin times were independent univariant and multivariant predictors of bleeding after CPB (r = 0.554, p = 0.0002 and r = 0.655, p = 0.00001).'] Does platelet glass bead retention predict bleeding after cardiac surgery?