Abnormalities of platelet haemostasis pose increased risk to patients undergoing anaesthesia and surgery. We have investigated the effect of propofol on platelet aggregation in 12 patients undergoing upper and lower abdominal surgery. Propofol 2.5 mg kg-1 was administered via a cannula in the antecubital vein. Venous blood samples were obtained before induction and 10 min after administration of propofol. Platelet aggregation measurements were made for adenosine diphosphate (ADP), collagen and adrenaline. The results show that propofol does not affect platelet aggregation in the concentrations used.