ATP-stimulated prostacyclin release from veins was investigated using epigastric veins isolated from hamsters. Veins were perfused with MOPS-buffered PSS. ATP was administered into the perfusate and the bath solution (MOPS-PSS) was collected and assayed for the presence of the stable prostacyclin metabolite, 6-keto-PGF₁. ATP (100 µM) resulted in reproducible increases in bath concentration from 73 ± 22 to 279 ± 50 pg/ml (P<0.05, n=5). This response was abolished by indomethacin (10 µM, P<0.05). To ascertain whether the endothelium was the source of prostacyclin, endothelium was disrupted using air (n=10) or deoxycholic acid (n=6). Perfusion with air significantly reduced (P<0.05) but did not completely abolish ATP-stimulated release of prostacyclin, while deoxycholic acid totally abolished the response (P<0.05). The non-selective P2 receptor antagonist reactive blue 2 (100 µM) attenuated ATP-mediated release of prostacyclin, but did not significantly alter ACh-stimulated release of prostacyclin. The non-selective adenosine receptor antagonist, xanthine amine congener (1 µM) had no effect on ATP-stimulated release and adenosine did not stimulate the release of prostacyclin. These results show that increases in intraluminal concentration of ATP stimulate abluminal release of prostacyclin from the venous endothelium. This effect is mediated by P2 receptors while adenosine and its receptors are not involved in this response.