soy isoflavones show antioxidant and estrogenic effects and have been related to decreased risk of cancer and cardiovascular diseases. the goal of the present study was to standardize the extraction of isoflavones from soy molasses and to evaluate the plasmatic and urinary concentrations of isoflavones in rabbits after consumption of extracted isoflavones. isoflavones were extracted with 90% ethanol and purified with a c18 column. the extraction yield was 81%. the purified isoflavone extract was added to the chow (5 mg isoflavone/ kg body weight/ day) used for feeding rabbits during 6 months. the concentration of isoflavones (genistein and daidzein) in the extracts, chow, blood plasma and urine was determined by high performance liquid chromotagraphy. the mean concentration of isoflavones in blood plasma was 4 mm and the urinary excretion was 22 μmol/24 h. the extraction of isoflavones from soy molasses resulted in a suitable preparation for experimental studies.