Abstract: Farrerol is one of the expectorant principles isolated from the aqueous extract of the leaves of Rhododendron dauricum L. The expectorant action and some other pharmacological activities of farrerol were reported in a previous paper. In the present article, some results on the metabolism of farrerol are reported.Farrerol in biological materials was extracted with ether at pH 6 and assayed spectrophotometrically in alkaline solution at 335 nm. This method was shown to be simple, sensitive and specific for the quantitative determination of farrerol in biological materials.Seventy to eighty per cent of the dose disappeared from the gastrointestinal tract 6～12 hours after oral administration of farrerol to rats. About thirty per cent of the dose was recoyered in the feces collected for four days. Low drug level (9.2μg/gm tissue) was found in the liver and only trace amounts of the drug were detected in the brain, blood and fat one hour after an oral dose of 200 mg/kg. After intravenous administration the highest drug level was found in the lungs, and the levels decreased in the order of brain, liver, kidneys, spleen, heart and fat, with the lowest level in the blood. Only 1.6 per cent of the drug was recovered in the five-day urine sample after a single oral dose. A great part of the drug was metabolized rapidly in the body, and the liver was shown to be the chief organ for the metabolism of farrerol.In addition to unchanged drug, four metabolic products of farrerol were isolated from the urine of drug-treated rats, one of them was considered to be the glucuronic acid conjugate of farrerol.