A chymostatin-sensitive angiotensin II-generating enzyme was found in human gastroepiploic arteries. The enzyme was purified using heparin affinity and gel filtration columns. The molecular mass of the purified enzyme was 30 kDa, and the optimum pH was between 7.5 and 9.0. Enzyme activity was inhibited by soybean trypsin inhibitor, phenylmethylsulfonyl fluoride and chymostatin, but not by ethylenediaminetetraacetic acid, pepstatin and aprotinin. The enzyme rapidly converted angiotensin I to angiotensin II (K(m), 67 mumol/l; Vmax, 43 pmol/s, kcat, 65/s), but did not hydrolyse angiotensin II, substance P, bradykinin, vasoactive intestinal peptide, luteinizing hormone-releasing hormone, somatostatin and alpha-melanocyte-stimulating hormone. The N-terminal sequence was identical to the sequence for human skin/heart chymase. Thus, the chymostatin-sensitive angiotensin II-generating enzyme in human vascular tissues is identified as chymase.