AbstractThe relative merits of gluteraldehyde tanned human umbilical vein (HUV) and polytetrafluorethylene (PTFE) as alternative arterial grafts have yet to be distinguished in clinical practice. A direct comparison between the thrombogenicity of these rival materials using human blood in an artificial circulation has therefore been made. Eight volunteers each donated 600ml of blood. The heparinized blood, now containing autologous113Inmlabelled platelets, was divided equally into paired artificial circulations incorporating 15 cm lengths of either 6 mm PTFE or HUV. The grafts were perfused for 45 min with a pulsatile flow mimicking the superficial femoral artery. Platelet deposition on the graft (graft activity) was expressed as the ratio of counts from the graft over those per millilitre of blood. The fall in platelet count over the 45‐min period and change in threshold aggregation responses were also measured. Platelet deposition was consistently greater on HUV with a mean (±s.e.) graft activity of 5·59±0·9 markedly exceeding that in the PTFE group of 1·16±0.1 (P<0·01). This increased consumption of platelets by HUV was demonstrated by a mean fall in platelet count in the circulating blood of 46·7±8·4 × 109/1 compared to a fall of 18·2 ± 6·2 × 109/l in the PTFE group (P<0·01). Furthermore, aggregation thresholds increased more after exposure to HUV compared to PTFE. The flow surface platelet deposition was confirmed by scanning electron microscopy and in addition patchy subintimal dissection was found in all the HUV grafts. HUV is markedly more thrombogenic than PTFE when examined in an artificial circulation under flow conditions similar to the human femoro