The plasma reserve albumin concentration for binding of bilirubin was found to be low in four newborn infants with deficiency of bilirubin excretion, of whom two had the bronze baby syndrome. Thus, the risk of bilirubin encephalopathy was increased. Also the ratio of binding fraction of albumin, i.e. unconjugated bilirubin plus reserve albumin, to total albumin was low. Possible causes of the low reserve albumin concentration and the ratio are discussed.