The effects of i. v. infusion of 5% albumin and balanced salt solutions were investigated in a prospective study on 18 patients subjected to reconstruction of the abdominal aorta. The same schedules for blood replacement and intraoperative fluid therapy were followed for all patients. Postoperatively, the amounts of fluid administered were adjusted with the aim of keeping the mean pulmonary arterial occlusion pressure (MPAOP) close to the preoperative level. Immediately after operation, there was a decrease in cardiac filling pressures, indicating a blood volume deficit, in both groups. Less fluid was needed for adequate haemodynamic restitution in the albumin group. Postoperatively, the mean plasma oncotic pressure (POP) in the albumin-treated patients remained steady at 2.4-2.5 kPa (86–88% of preoperative value). In the control group, POP fell to a mean minimum of 1.8 kPa (64% of preoperative value) 8 h after operation. The difference between POP and MPAOP decreased significantly in both groups, but the difference between the groups was not significant at any time. There was no significant correlation between venous admixture, on the one hand, and POP, MPAOP, POP-MPAOP difference, total sodium intake or net supply of non-colloid fluids, on the other. No clinically important differences in haemodynamic or lung function variables were found between the groups.