The assessment of reserve bilirubin binding capacity of serum in 12 children with type I Crigler-Najjar syndrome was performed by 3 biochemical methods. Two of them use chromatography techniques: thin layer on Sephadex or high performance liquid; they allow the determination of the saturation rate of all serum bilirubin carriers. The third method only evaluates the major carrier, albumin, using the molar bilirubin-albumin ratio. An identical correlation coefficient of 0,90 has been obtained when comparing with the chromatographic method on thin layer, respectively 20 determinations using high performance liquid chromatography and 122 measurements of the bilirubin/albumin ratio. In practice, we advise a first, simple and rapid determination of the bilirubin/albumin ratio in case of a sudden aggravation of the jaundice in the children with Crigler-Najjar type I disease. The chromatographic methods will be used in a second step, or in order to survey the phototherapy treatment that these children receive.