Oral administration of Yin Zhi Huang (YZH) daily for 3 days in rabbits accelerated plasma clearance of infused unconjugated bilirubin. A similar but less dramatic effect resulted from 3 days pretreatment with phenobarbital, 70 mg/kg/day orally. Similar doses were injected intraperitoneally in rats for 3 days, following which the bile ducts were ligated and bilirubin infused intravenously. Plasma clearance of unconjugated bilirubin and plasma appearance of conjugated bilirubin were faster, and hepatic bilirubin content was higher in both YZH- and phenobarbital-treated rats than in control animals. These observations indicate that YZH is as effective as phenobarbital in stimulating bilirubin metabolic pathways and suggest that the drugs may share common mechanisms of action.