The kinetic parameters of indocyanine green elimination from blood were determined after an intravenous load of the dye in a dosage of 2-4 mg per kg body weight in 22 newborns with a non-hemolytic hyperbilirubinemia. Since the uptake of indocyanine green by liver is selectively carried out and the dye is not further metabolised, these kinetic parameters serve as measures for the performance of hepatocellular elimination. 11 of these newborns were treated 5 days previously with 7.5 mg phenobarbital per kg body weight. Compared to the untreated group, the serum bilirubin concentration significantly decreased after treatment with phenobarbital and the parameters of elimination of the dye from blood changed as described by saturation-kinetics. The maximal elimination-rate Vmax and the Michaelis-Menten-constant Km were significantly higher in newborns treated with phenobarbital (71.1 muMol/l-min and 356.4 muMol/l) than in the untreated ones (23.4 muMol/l-min and 100.0 mutmol/l). Kinetic data of indocyanine green elimination gathered in newborns treated with and without phenobarbital support the hypothesis that cytoplasmatic proteins oliver should facilitate the uptake of organic anions inclusively bilirubin into the liver cell. A defiency of such transport proteins may be one of the causes of non-hemolytic hyperbilirubinemia in newborns.