All patients admitted to an Intensive Care Unit were assigned randomly to one of two groups, A and B. Group A received colloid volume replacement as 4.5% albumin whilst group B received a synthetic colloid, polygeline. This study describes the changes in serum albumin concentration in survivors and nonsurvivors in the two groups during their stay in the Intensive Care Unit. The incidences of renal failure and pulmonary oedema were also assessed. Serum albumin concentration decreased in all nonsurvivors. In survivors the serum albumin concentration decreased to a greater extent in the synthetic colloid group than in the albumin group. Despite the differences in serum albumin concentration there were no significant differences between the groups in the incidences of pulmonary oedema or renal failure.