Examination was made of the urinary and biliary excretion of the metabolites of puerarin, the major component of the roots of Pueraria lobata OHWI (Leguminosae) in rats. The urine of rats administered puerarin orally contained puerarin and four major metabolites, daidzein 4',7-di-O-sulfate (M-I), daidzein 7-O-beta-D-glucuronide (M-II), daidzein 4'-O-sulfate (M-III), daidzein (M-IV), as determined from spectroscopic and chemical data. Total cumulative amounts of the puerarin and four metabolites excreted in the urine at 48 h following the oral administration of puerarin were approximately 3.6% the doses administered. The bile of rats administered puerarin orally contained puerarin and two major metabolites, which were identified as puerarin 4'-O-sulfate (PB1) and puerarin 7-O-beta-D-glucuronide (PB2) on the basis of chemical and spectroscopic data. These experimental data suggest that C-glycoside puerarin is partially hydrolyzed to aglycone in the body, but mainly excreted in the urine as unchanged puerarin.