Ile-Trp (IW) and Trp-Leu (WL) are present in enzymatic hydrolysates of whey proteins and act as efficient inhibitors for angiotensin-converting enzyme (ACE) in vitro. Baseline plasma concentrations of IW and WL were analysed to 0.9 +/- 0.3 nm for IW and 8.3 +/- 1.3 nm for WL Following administration of 50 mg IW or 100 mg WL to human volunteers (n = 3 for IW and n = 2 for WI, respectively), a significant increase in plasma concentrations to a maximum of 2.4 +/- 0.5 nm for IW and 29-36 nm for WL after 0.5 h was observed, followed by rapid elimination. ACE activity in plasma decreased by 32% +/- 8% following 50 mg IW administration. Administration of the corresponding amino acids had no effect on ACE activity. Thus, these tryptophan-containing dipeptides may serve as bioactive food additives with beneficial effects for the cardiovascular system. (C) 2015 Elsevier Ltd. All rights reserved.