The ACE inhibitory activity in red-mold rice extracts, prepared from 24 strains of the genus Monascus, was measured. The most effective strain for ACE inhibition was Monascus purpureus IFO 4489 (IC(50) = 0.71 mg/ml). Although the antihypertensive substance gamma-amino butyric acid was detected in the red-mold rice (85.2 mg/kg), it did not contribute to ACE inhibition. Four ACE inhibitory peptides were isolated from the extract and identified as Ile-Tyr (IC(50) = 4.0 mu M), Val-Val-Tyr (22.0 mu M), Val-Phe (49.7 mu M) and Val-Trp (3.1 mu M) by protein sequencing. The ACE inhibitory activity of these peptides was almost completely preserved after successive in vitro digestion by pepsin, chymotrypsin and trypsin. These results suggest that red-mold rice made by M. purpureus could be useful in alleviating hypertension. (C) 2009 Elsevier Ltd. All rights reserved.