We have demonstrated that the isolated perfused rat mesenteric arterial bed (MAB) secretes peptidases capable of metabolizing bradykinin and angiotensin I. The major degradative pathway of bradykinin by enzymes found in the rat MAB perfusate was mediated by carboxypeptidase A-like activity, whereas angiotensin 1 degradation followed two main routes, one attributable to a carboxypeptidase A-like enzyme and the other to an endopeptidase. This latter enzyme seems to be a novel serine peptidase capable of releasing angiotensin II directly from both angiotensin I and renin substrate tetradecapeptide. The rat MAB perfusate was also shown to contain additional endo- and exopeptidases that might play a role in the metabolism of other vasoactive peptides. Our finding that isolated rat MAB secretes peptidases into the perfusion medium indicates that peptide processing within the microvasculature environment may be effected by enzymes besides those normally found in plasma or associated with cell membranes.