The renin-angiotensin system (RAS) is one of the main control systems of arterial blood pressure. Here, key player is the angiotensin converting enzyme (ACE). Inhibition of ACE is a standard therapy to lower elevated blood pressure. This study aimed to determine the ACE-inhibitory activity of tryptophan- and tyrosine-containing peptide mixes, based on hydrolysates of whey-, soy- and rice-protein. Effects on circulating and tissue ACE were investigated. IC₅₀ values range from 16.60 ± 2.59 mg/l to 282.04 ± 18.51 mg/l, depending on the peptide mix and the ACE-system. Strongest ACE-inhibition is generally obtained with whey peptide mix characterized by a high fraction of isoleucine-tryptophan. Good inhibitory potential was obtained for plasma and tissue ACE. Thus, the use of whey peptide mix and isoleucine-tryptophan, respectively, appears to deserve further studies as innovative food additives with the potential to delay or even prevent RAS-related hypertension and subsequent deterioration of vessel structure and function.