Cassiae Semen (seeds of Cassia tora) showed a remarkably different HPLC chromatogram after being treated with a crude enzyme extract from Aspergillus usamii. Increased and decreased compounds were identified as aurantio-obtusin and glucoaurantio-obtusin, respectively. The aurantio-obtusin content reached its maximum level (133.58 +/- 0.39 microg/mg extract) after being incubated for 50 min at 37 degrees C, whereas the inactivated crude enzyme-treated control remained unchanged (54.13 +/- 1.33 microg/mg). On the other hand, the glucoaurantio-obtusin content decreased by less than one-third (51.09 +/- 1.63 microg/ mg) of the untreated control (143.19 +/- 2.12 microg/mg), suggesting that an increase in aurantio-obtusin content originated from the enzymatic cleavage of its glucoside glucoaurantio-obtusin.