Adrenomedullin (AM) is a novel and potent vasodilator peptide originally isolated from human pheochromocytoma. The present study was designed to study whether AM is produced by and secreted from renal tubular cell lines and whether arginine vasopressin (AVP) affects AM secretion from these cell lines. Three renal tubular cell lines derived from different species (LLCPK1, MDCK, and MDBK) secrete AM-like immunoreactivity (AM-LI) into culture medium, the immunological and physicochemical properties of which are similar to that of synthetic human AM as evaluated by reverse-phase high-performance liquid chromatography. Among the three cell lines, AVP in combination with a phosphodiesterase inhibitor (isobutylmethylxanthine) stimulated AM-LI secretion most potently from MDCK cells in a time- and dose-dependent manner. In MDCK cells, a V<sub>2</sub> receptor agonist (deamino- D-Arg<sup>8</sup>-vasopressin) dose-dependently stimulated AM-LI secretion in the same manner as AVP. Furthermore, the AVP-induced AM-LI secretion was blocked by a V<sub>2</sub> receptor antagonist (OPC31260), but not by a V<sub>1</sub> receptor antagonist (OPC21268). These data indicate that AM is secreted from renal tubular cell lines and that AVP stimulates AM secretion via V<sub>2</sub> receptors, suggesting its autocrine/paracrine role in renal function.