The pharmacologic management of hemostasis in patients undergoing cardiopulmonary bypass may be accompanied by adverse responses. Evaluating the safety profile of hemostatic agents (eg, lysine analogs, aprotinin, protamine, or even donor blood) should be done objectively. Subsequent to early anecdotal reports, the safety profile of aprotinin, a broad-spectrum serine protease inhibitor, has been thoroughly evaluated in multiple double-blind, placebo-controlled, multicenter studies. Although associated with decreased fibrinolysis, aprotinin has not been associated with an increased risk of post-cardiopulmonary bypass myocardial infarction, graft closure, stroke, or increased risk of renal dysfunction from US studies. As with any polypeptide, there is a risk of anaphylaxis, which is influenced not only by prior exposure but also by time since prior exposure. In a similar fashion, after early anecdotal reports, evaluations involving large numbers of patients have helped define adverse reactions to protamine. Adverse reactions to blood products also must be considered in any safety comparisons involving hemostatic agents.