We have developed an in vitro haemoperfusion circuit, which closely simulates the conditions encountered in a clinical haemoperfusion, for testing the blood compatibility of new adsorbent materials. Fresh heparinised human blood is perfused for 2 hours over two model columns arranged in parallel closed circuits. The present study was performed to investigate the blood compatibility of human serum albumin-coated Amberlite XAD-7 resin. Mean platelet losses over 2 hours were greater following perfusion of the uncoated resin (44 +/- SE 5.6%) than the albumin-coated resin (17 +/- SE 2.2%) (p less than 0.01). Mean white cell losses were similar (55%) for both resins. No rises in Swank screen filtration pressure, which detects the presence of cellular aggregates in blood, were observed. Coating of XAD-7 resin with HSA therefore improves its blood compatibility with respect to platelet losses and we thus intend to use this preparation in a clinical trial of resin haemoperfusion in fulminant hepatic failure.