Prostacyclin (PGl2), the most potent and short-lived antiplatelet agent known today, has been used successfully as an antithrombotic in hemodialysis (HD). However, its vasodilatory effect has been the source of blood pressure instability in acetate HD and has restricted its use to bicarbonate HD. The authors took advantage of the better cardiovascular stability obtained with hemofiltaration (HF) to compare the effects of PGI2 versus heparin either with acetate or bicarbonate HF in 4 patients. Efficacy of PGI2 in preventing thrombosis of the extracorporeal circuit was demonstrated in all cases with a dose of 4 ng/kg/min. HF performances remained unaffected whatever antithrombotic agent was used. Platelet activation as shown by BTG and PF4 release was inhibited by the PGI2 infusion. Platelet proteins release was greater with acetate HF, suggesting that acetate may have a specific role in platelet activation. Although the use of PGI2 was straightforward, it is worth noting that PGI2 partially suppressed the cardiostability usually associated with acetate HF. We conclude that the efficacy of PGI2 was well maintained in spite of conditions of high platelet shear stress conditions, but also that PGI2 potentiated the vasodilatory effect of acetate and suppressed partially the cardiovascular benefits of HF.