Objective To invistigate molecular mechanism of the effect of aprotinin on platelets membrane glycoproyin during cardiopulmenary bypass Methods The venous blood of 20 healthy volunteers in the tubes containing 3 2% trisodium citrate or 5u/ml heparin,to evaluate the effect of aprotinin on the expressions of platelets membrane glycoprotein (GP) Ⅱb Ⅲa receptor and P seclectin with flow cytometric analysis Results Aprotinin at 50 200U/ml decreased the expression of activated GP Ⅱb Ⅲa complex in response to adenosine diphosphate or thrombin receptor activator peptide 6 in a dose dependent manner in both citrated and heparinized whole blood experiments (P