Plasma clearances of sulfobromophthalein sodium (BSP), indocyanine green (ICG) and unconjugated bilirubin were studied in six patients with Rotor's syndrome. A marked retention of these three substances in the plasma was observed. At 60 minutes after injection, serum BSP consisted almost entirely of the unconjugated form. In three patients, BSP Tm and BSP S were significantly reduced. Clearance of unconjugated bilirubin was markedly impaired. This, together with the conjugated hyperbilirubinemia may be interpreted to reflect reduced storage. These results indicate that Rotor's syndrome is marked by reduced hepatic storage capacity and excretory function of BSP, ICG and bilirubin.