The protective effect of Pycnogenol against cardiovascular diseases was clearly demonstrated. Nevertheless, little is known about its antithrombotic effect, especially in diabetes associated with enhanced thromboxane synthesis leading to severe vascular complications. Therefore, the main purpose of our study was to evaluate the effect of long-term Pycnogenol intake on synthesis of prothrombotic thromboxane A(2) (TXA(2)) in animal model of insulin-dependent diabetes. The levels of main plasma TXA(2) metabolite, thromboxane B(2) (TXB(2)), were assessed by enzyme-linked immunosorbent assay. Diabetes was induced in Wistar male rats by single injection of streptozotocin, resulting after 8 weeks in significant body weight reduction, increased plasma glucose concentrations, and decreased plasma C-peptide levels, compared to non-diabetic animals. There was no significant reduction of plasma glucose concentrations after Pycnogenol ingestion. It was found, however, that daily administration of either Pycnogenol (5mg/kg b.wt.) or acetylsalicylic acid (ASA, 10mg/kg b.wt.) significantly reduced plasma TXB(2) concentrations, and this inhibitory effect was higher in the latter case. Nonetheless, simultaneous administration of Pycnogenol and ASA did not improve effectiveness of ASA-mediated decrease in TXB(2) generation. The results of the present study suggest that Pycnogenol might have a beneficial antithrombotic effect when administered alone or as a supplementation of standard antiplatelet therapy in diabetic patients.