We evaluated expression of platelet activation markers in blood samples of 15 patients who underwent percutaneous transluminal coronary angioplasty (PTCA) by flow cytometry. Analysis was performed before the beginning of PTCA, during initial coronary angiography and after the end of PTCA or after a stent placement, respectively. We evaluated platelet-derived microparticles, platelet-leukocyte aggregates, platelet aggregates and a membrane expression of CD62P and CD63 molecules. Responsiveness of platelets to the activation in vitro with thrombin-receptor activating protein-6 (TRAP-6) was tested simultaneously. Statistically significant differences between patient samples were found only in the expression of the activation markers CD62P (before PTCA 0.22%, during 0.39%, after 0.67%), CD63 (0.26%/0.45%/0.85%) and platelet-leukocyte aggregates (13.57%/18.39%/23.63%). In the same group the expression of all constitutive membrane markers was statistically significantly decreased: in patients undergoing PTCA was the expression of CD9: 87.98% (in comparison with control group 94.98%), CD31: 87.10% (92.78%), CD36: 87.37% (90.98%), CD41: 88.09% (95.62%), CD42a: 88.54% (94.98%), CD42a: 88.31% (94.13%).