Whey protein concentrate (WPC) hydrolysates generated using Neutrase (R), Alcalase (R) and Flavourzyme (R) and their associated ultrafiltration fractions inhibited angiotensin-1-converting enzyme activity (71.14 +/- 1.05, 73.22 +/- 0.99 and 51.52 +/- 5.80% inhibition when assayed at 14.3 mu g/rnL). Incubation of human umbilical vein endothelial cells with 5 kDa permeates of Neutrase (R)- and Alcalase (R)-hydrolysed WPC for 48 h resulted in the beneficial differential expression of genes relevant to blood pressure control, as measured by microarray. Furthermore, real-time reverse transcriptase polymerase chain reaction demonstrated an upregulation of endothelial nitric oxide synthase (+2.14 +/- 0.45 and 2.36 +/- 0.27-fold) and down-regulation of endothelin-1 (0.58 +/- 0.09 and 0.82 +/- 0.11-fold) following incubation with the 5 kDa permeates of Alcalase (R)- and Neutrase (R)-hydrolysates, respectively. Peptide sequences within the 5 kDa permeate of the Alcalase (R)-hydrolysed WPC were identified, many of which have previously been demonstrated as having ACE-inhibitory and/or other bioactivities. These WPC hydrolysates potentially represent sources of bioactive peptides for the beneficial regulation of endothelial cell function.