This article reports the evidence and the biochemical properties of an angiotensin-converting (ACE)-like enzyme from head parts of the leech Theromyzon tessulatum. After solubilization from membranes with Triton X-114, the ACE-like enzyme was purified from the detergent-poor fraction. Four steps of purification including gel permeation and anion exchange chromatographies followed by a reversed-phase HPLC were needed. This poor glycosylated peptidyl dipeptidase (of ca. 120 kDa) hydrolyzes, at pH 8.4 and at 37°C, the Phe 8 -His 9 bond of angiotensin I with a high catalytic activity (i.e., K m : 830 μM and K c a t /K m : 153 s - 1 mM - 1 ). The hydrolysis of angiotensin I is inhibitable at 80% by captopril (IC 5 0 = 175 nM) and lisinopril (IC 5 0 = 35 nM). This activity is strictly dependent on the presence of NaCl and is increased by Zn 2 + . This zinc metallopeptidase also attacks peptides that have in their sequence either Gly-His, Gly-Phe, or Phe-His bond [e.g., enkephalins (K c a t /K m : 12 s - 1 mM - 1 ) or bradykinin (K c a t /K m : 2200 s - 1 mM - 1 ]. Taken together, these arguments are consistent with an ACE-like activity implicated in metabolism of angiotensins and bradykinin in leeches.