The behaviour of some cholephilic anions has been studied in three male patients (two of whom are brothers) affected with Rotor syndrome. The unconjugated bilirubin clearance was markedly reduced with impairment of the plasma-liver transfer constant rate (uptake defect). BSP retention at 45 min. was elevated without late rise of the anion. Transport maximum (" Tm") of BSP was slightly reduced; relative hepatic storage capacity of BSP (" S") was significantly impaired. Plasmatic retention of 131-I-Rose Bengal was increased with a diminished hepatic uptake of the compound. The hepatic excretion of IDA-derivatives was impaired, but less for parabutyl-IDA than for diethyl-IDA. It is concluded that in Rotor syndrome there exists an alteration of uptake and storage of several cholephilic organic anions: the alteration is common not only to substances that undergo intracellular conjugation--such as bilirubin and BSP--but also to substances that are not metabolized--such as Rose Bengal and IDA--derivatives. Finally the authors suggest that the Rotor syndrome and so--called" Hepatic storage disease" are the same condition.