Haemodialysis was performed using heparin (dialysis I: heparin regimen 1, 2000 U/h) in ten patients. These subjects were then given an infusion of prostacyclin, in the form of epoprostenol sodium salt (dialysis II: prostacyclin, 5 ng X kg-1 X min-1), followed by an infusion of prostacyclin and heparin (dialysis III: heparin regimen 2,500 U/h). Absolute platelet count, in vitro platelet aggregation and plasma beta-thromboglobulin decreased during prostacyclin infusion. Haemodialysis neutropenia was improved by prostacyclin. The membrane sieving coefficient factor and ultrafiltration volume were not improved by prostacyclin alone (dialysis II). Prostacyclin together with heparin (dialysis III) showed, 60 minutes after the start, an unchanged sieving coefficient factor compared with that of heparin alone, while the ultrafiltration volume significantly (P less than 0.001) improved. The results of this study confirm those of earlier studies and suggest that prostaglandin I2 together with low-dose heparin improve the biocompatibility and efficiency of dialysis treatment.