Angiotensin I-converting enzyme (ACE) inhibitory peptides were isolated and characterized from cowpea (Vigna unguiculata L walp). Cowpea protein isolate was prepared by wet fractionation, extensively hydrolyzed with Flavourzyme and filtered through four molecular weight cut-off (MWCO) membranes in a high performance ultrafiltration (UF) cell. The ultrafiltered fraction with the highest ACE inhibitory activity was purified using gel filtration chromatography followed by reverse-phase high performance liquid chromatography (RP-HPLC). The cowpea peptide inhibition (IC50) values were similar to those reported for many other natural ACE inhibitory peptides. The < 1 kDa ultrafiltered fraction exhibited the highest biological activity. The observed amino acid composition suggests a substantial contribution of hydrophobic residues to the peptides' inhibitory potency, which potentially acts via blocking of angiotensin II production. When hydrolyzed with the protease Flavourzyme, cowpea V. unguiculata protein is a good source of ACE inhibitory peptides with potential applications in physiologically functional foods with antihypertensive activity. (c) 2010 Elsevier Ltd. All rights reserved.