Thirty patients undergoing major hepatobiliary or pancreatic surgery were randomly allocated to receive either 0.9% saline or Plasmalyte 148 (a balanced salt solution), at 15 ml.kg-1.h-1. Arterial blood gas analysis was performed before and after surgery. Plasma biochemistry (Na+, K+, Cl-, lactate) measurements were made before and after surgery and at 24 h after surgery. The patients receiving 0.9% saline had significantly increased chloride concentrations (p < 0.01), decreased standard bicarbonate concentrations (p < 0.01) and increased base deficit (p < 0.01) compared to those receiving Plasmalyte 148. There were no significant changes in plasma sodium or potassium or blood lactate concentrations in either group. The exclusive use of 0.9% saline intra-operatively can produce a temporary hyperchloraemic acidosis which could be given false pathological significance. In addition it may exacerbate an acidosis resulting from an actual pathological state. The use of a balanced salt solution such as Plasmalyte 148 may avoid these complications.