Yin Zhi Huang (YZH) is a decoction of four plants which is widely used in Asia to treat neonatal jaundice. This study compares the ability of phénobarbital and the individual herbs comprising YZH, Artemisia, Gardenia, Rheum, and Scutellaria baicalensis, to induce hepatic drug and bilirubin metabolizing enzymes in rats. Herbal decoctions (30 ml/kg/day) or phénobarbital (60 mg/kg/day) were administered for 5 days. Only phénobarbital increased cytochrome P-450 levels whereas Gardenia slightly decreased levels. Artemisia, Rheum and phénobarbital increased bilirubin glucuronyl transferase activity. Glucuronidation of a-naphthol was increased by Gardenia and phénobarbital, whereas Artemisia and Rheum were ineffective inducers. Phénobarbital was the most effective inducer of glutathione-S-transferase (GSHT) activity. Phénobarbital and Gardenia both induced ∆(5)-3-ketosteroid isomerase activity, a marker for the Ya subunit of GSHT responsible for intracellular bilirubin transport in liver. The selective patterns of enzyme induction suggest potential value for using specific plant decoctions to modify drug and bilirubin metabolic pathways.