Nikolaos E Androulakis,1 Nikolaos E Koundourakis,2 Eleni Nioti,1 Paraskevi Spatharaki,1 Despina Hatzisymeon,1 Ioannis Miminas,1 Michael G Alexandrakis1,3 1Hematology Laboratory, Iraklion University Hospital, Iraklion, Greece; 2Department of Clinical Chemistry-Biochemistry, 3Department of Hematology, School of Medicine, University of Crete, Iraklion, Greece Aim: To examine whether a high volume of soccer-specific training can lead to endothelial activation and/or dysfunction in professional soccer players due to exercise-induced oxidative stress. Methods: Twenty-three (15 nonsmokers and eight smokers) healthy, elite male professional soccer players (mean age: 25.2±4.3 years, BMI: 23.1±1.3 kg/m2, fat: 7.8%±2.6%) were selected for this study. All participants had a full clinical and laboratory evaluation. von Willebrand factor antigen (vWf Ag) plasma levels were measured on two different occasions: 1 day before the beginning of the preseason preparation period and after 7 weeks of strenuous exercise. Results: Mean vWf Ag plasma levels were significantly decreased from 95.1%±26% to 88.3%±27.2% at the end of the experimental period (P=0.018), suggesting a potential beneficial effect on the endothelium of these athletes. Further analysis showed that age greater than 29 years with an age range from 29 to 34 years can not impair this effect (P>0.05). Conclusion: Strenuous exercise did not lead to endothelium activation or dysfunction in well-trained elite soccer players. On the contrary, it seemed to produce a beneficial effect on the endothelium of these players. Keywords: endothelium, strenuous exercise, smoking