We have studied the use of ultrapurified polymerized bovine haemoglobin (HBOC-201) in patients undergoing preoperative haemodilution before liver resection. After autologous blood donation of 1 litre, 12 patients (six males, six females, mean age 59 (35-69) yr) received Ringer's lactate solution 2 litre and, in a random design, 6% hydroxyethyl starch 70,000/0.5 (HES) 3 ml kg-1 or HBOC-201 0.4 g kg-1 within 30 min. Blood samples were obtained for blood chemistry, co-oximetry, haematology, coagulation profiles and immunology examinations before operation, on the day of surgery, on days 2-4 and 7 after operation, on the discharge day and 3 months after operation. There were no differences in patient characteristics, blood loss, amount of solutions infused, transfused allogeneic blood or duration of hospital stay. There were no local or systemic allergic reactions with infusion of HES or HBOC-201. Patients receiving HBOC-201 developed more pronounced leucocytosis and reticulocytosis during the early postoperative days compared with HES-treated patients. The mean maximum plasma haemoglobin concentration was 1.0 (SD 0.2) g dl-1 at the end of infusion of HBOC-201 was 8.5 h. Patients in both groups experienced temporary changes in liver enzymes and coagulation variables which returned to normal before discharge. Urinalysis revealed no difference between groups and no free haemoglobin was detected in urine. Patients receiving HBOC-201 showed no IgE and only a slight increase in IgG titres to HBOC-201 on the day of discharge; these were not detectable at 3 months. Single-dose administration of HBOC-201 was well tolerated by patients undergoing elective liver resection surgery and appears to be safe as a substitute during preoperative haemodilution.