Influence of bucolome on non-bilirubin fraction showing positive diazo-reaction (non-bilirubin fraction, dipyrril substances) was studied using heterozygous Gunn rats. Two hundred mg of bucolome per kg of rat body weight was injected intramuscularly once a day for four days. The bile collection by the bile duct canulation was started 24 hours after the final drug loading and continued for 22 hours. The following results were obtained: 1) Amount of non-bilirubin in the rat bile increased significantly in bucolome loading group than in the control group. 2) Radioactivity in non-bilirubin fraction in the bile after bucolome and (3)H-bilirubin loading was not increased significantly than in the control. 3) In bucolome loading group, bile volume increased significantly but the excreted amount of bilirubin did not increased. According to these results, bucolome did not catabolize bilirubin directly but increased non-bilirubin fraction, dipyrril substances, in the bile.