Hydroxyethyl starch (HES) is a recently developed synthetic volume expander. Forty patients undergoing coronary artery surgery were randomized to receive either HES or plasma protein fraction (PPF) as non-blood volume replacement according to standard haemodynamic criteria. The two groups were comparable in all respects. The median colloid use in the first 24 h was 950 ml (range 500-1500) in the HES group and 975 ml (350-2000) in the PPF group (not significant). There was no difference in blood use, urine output or blood loss between the two groups. Tests of coagulation showed the postoperative changes usual in cardiac surgical patients. There was no difference between the two groups in thrombin time, prothrombin time, activated partial thromboplastin time, or fibrinogen concentration. Similarly, tests of platelet function and Factor VIII and von Willebrand Factor activity showed no difference between the two groups. We conclude that HES is a safe and effective volume expander, and its relative lack of expense and ease of availability make its routine use after cardiac surgery an attractive proposition.