Xiexin decoction (XXD), a classic pyretolysis formula, is composed of Rhei Rhizoma (DH), Radix Scutellaria (HQ) and Coptis Chinensis (HL) and is commonly used in the clinical setting. The aim of this study was to investigate the pharmacokinetic differences of the five anthraquinones in rats after oral administration of XXD and different combinations of its constituent herbs. Twenty rats were randomly divided into four groups and were administered one of the four extracts: DH, DH-HQ, DH-HL and XXD (DH-HQ-HL) via intragastric gavage. Anthraquinone concentrations in plasma were determined by an HPLC technique. Pharmacokinetic parameters were calculated from the plasma concentration-time data. Compared with DH alone, the DH-HL combination decreased C(max) of all five anthraquinones and AUC of four anthraquinones (except physcion), and the DH-HQ combination decreased AUC of aloe-emodin and C(max) of rhein. Finally, XXD increased AUC of all five anthraquinones compared with DH-HL combination. These results showed that the oral bioavailabilities of five anthraquinones were decreased significantly by combining DH with HL, whereas HQ weakened the effect of HL that inhibited the absorption of anthraquinones. (c) 2008 John Wiley & Sons, Ltd.