The bleeding time is currently the only clinically available comprehensive test to explore primary hemostasis. It is currently performed mostly as a screening procedure before surgery, to detect otherwise unknown defects in platelet-vessel wall interactions, but its use in this specific setting has been seriously questioned by recent reanalyses of previously published literature. We studied the relationship of the bleeding time from a standardized cutaneous incision with other parameters of bleeding derived from the analysis of the bleeding time curve and prospectively investigated possible correlations of these alternative parameters, as well as of the bleeding time, with a number of indices of actual bleeding during or after coronary bypass surgery. Four parameters (bleeding time, total bleeding, peak bleeding rate, and time to peak bleeding) were derived from the analysis of bleeding time curves measuring blood losses from a standardized cutaneous incision at 30-second intervals in 118 subjects. Parameters from the bleeding time curve were subsequently obtained in duplicate as a preoperative assessment in 40 patients with a negative bleeding history and no recent intake of non-steroidal anti- inflammatory drugs who were undergoing elective pure coronary bypass surgery performed by the same operator. These parameters were correlated in simple linear regression analysis with estimates of surgical bleeding (chest tube drainage, transfusion requirements, percentage of hematocrit, percentage of platelet level decrease, and times to hematocrit and platelet level nadir) and then, in multiple regression analysis, with indices of operation complexity (number of bypasses, total duration of the operation, and duration of the extracorporeal circulation). Bleeding time was significantly correlated, among parameters derived from the bleeding time curve, with total bleeding and peak bleeding rate, but not with time to peak bleeding. Bleeding time, total bleeding, and peak bleeding rate were similarly affected by acute interventions with intravenous aspirin (500 mg) and sublingual nitroglycerin (0.3 mg). None of these parameters, which were obtained in duplicate in each patient preoperatively, was significantly related to actual indices of bleeding at surgery. Thus, in patients with a negative history of bleeding and no recent intake of non-steroidal anti-inflammatory drugs, higher values for bleeding time and bleeding time-related parameters are not associated with higher indices of perioperative and postoperative bleeding at coronary bypass surgery. Therefore, we do not recommend the use of the test in this setting to predict perioperative or postoperative bleeding.