Absorption, distribution and elimination of 14C-labelled isoflavone-containing extracts from kudzu (Pueraria lobata) root culture and red clover (Trifolium pratense) cell culture were investigated in an in vivo rat model. The predominant isoflavones in the kudzu extract were the glycosides puerarin, daidzin and malonyl daidzin, while in the red clover extract, the major isoflavones were formononetin and its derivatives, genistein and biochanin A, with radioactivities of 3·770 and 7·256 MBq/g, respectively. Male Sprague–Dawley rats, implanted with a jugular catheter and a subcutaneous ultrafiltrate probe, were orally administered with 14C-labelled isoflavone extracts from either kudzu or clover cell cultures. Serum, interstitial fluid (ISF), urine and faeces were collected using a Culex® Automated Blood Collection System for 24 h. Analysis of bone tissues revealed that radiolabel accumulated in the femur, tibia and vertebrae at 0·04, 0·03 and 0·01 % of the administered dose, respectively, in both kudzu and red clover treatments. The liver accumulated the greatest concentration of radiolabel among the tissues tested, at 1·99 and 1·54 % of the administered kudzu and red clover extracts, respectively. Serum and ISF analysis showed that both extracts were rapidly absorbed, distributed in various tissues, and largely eliminated in the urine and faeces. Urine and faeces contained 8·53 and 9·06 % of the kudzu dose, respectively, and 3·60 and 5·64 % of the red clover dose, respectively. Serum pharmacokinetics suggest that extracts from kudzu may undergo enterohepatic circulation.