Propofol has been reported to affect blood coagulation. This prospective, randomized study compared coagulation and blood loss during anaesthetic maintenance with target-controlled intravenous propofol infusion vs. inhaled isoflurane. Thirty-eight ASA I-III patients undergoing head and neck surgery were allocated randomly to receive either inhaled isoflurane at end-tidal concentration 1-1.5% (group I, n=20) or target-controlled infusion (TCI) of propofol at target concentration 2-5 microg ml(-1) (group P, n=18). Thrombelastography on recalcified whole blood was performed pre-induction, and at 15, 30, 60, 90, 120 min post-induction and 30 min after anaesthesia in both groups. Blood loss was estimated from weighing swabs and the volume in suction bottles. Induced hypotension was not used, and perioperative body temperature was similar between groups. There were no significant differences in thrombelastographic coagulation (R-time, K-time, maximum amplitude and angle) or fibrinolytic variables (lysis index at 30 and 60 min) at all times between groups. Total blood loss was also not significantly different (median group I: 350 ml, range 20-1200 ml; group P: 200 ml, range 50-800 ml). Shortening of R-time and widening of angle developed over time in both groups (P<0.05 groups I and P, repeated measures ANOVA). We conclude that maintenance of anaesthesia with propofol TCI at 2-5 microg ml(-1) does not cause detectable coagulation changes on thrombelastography nor increase surgical blood loss when compared to inhaled isoflurane.