The purpose of this study was to investigate the thromboembolic properties of ionic and nonionic contrast media in rats pretreated with aspirin and/or fraxiparine using an experimental model of laser induced thrombosis in the mesenteric microvessels of 17 groups of five male Wistar rats each. Two ionic (ioxaglate and diatrizoate) and two nonionic contrast media (iopamidol and iohexol), alone or associated with antithrombotic drugs (aspirin and/or fraxiparine) were studied. To evaluate the effects of these substances in this model, the number of laser beams needed to induce platelet thrombus formation, the number of emboli detached from the thrombus and the duration of embolization were quantified. Platelet aggregation induced by ADP, induced hemorrhagic time (IHT) and haemoglobin loss level were also determined. Both contrast media injected at 3 ml/kg caused a significant increase in the number of emboli and the duration of embolization (p<0.05). Pretreatment with aspirin and/or fraxiparine in the presence of ionic contrast media showed antithrombotic activities equal to those obtained when they were tested alone (p<0.05), while in the presence of nonionic contrast media, these drugs only neutralised the prothrombotic effects. There were no differences with the NaCl treated group (p>0.05). The ionic contrast media, and to a lesser extent the nonionic contrast medium: iohexol, inhibited platelet aggregation, while iopamidol behaved as an activator. The antithrombotic drugs tested in this study prevent the prothrombotic activities of contrast media therefore suggesting their use before radiographic procedures.