To study vasopressin receptor-mediated endocytosis using electronmicroscopy methods and to develop avidin affinity columns for receptor purification, we synthesized and tested the biological properties of a biotinylated vasopressin (VP) analog [1-(2-mercapto) propionic acid] 8-[lysine-N6-biotin] VP (B-MLVP). B-MLVP was prepared by coupling biotin to the epsilon amine of the lysine residue in [1-(2-mercapto) propionic acid] 8-(lysine) VP (MLVP). The structure of HPLC purified B-MLVP was confirmed by fast atom bombardment mass spectrometry. B-MLVP effectively competed for arginine vasopressin (AVP) binding sites in canine renal plasma membranes on the surface of LLC-PK1 kidney cells. Dissociation constants of 15 nM and 202 nM were calculated from the results of competition binding assays conducted with membranes and cells, respectively. B-MLVP stimulated adenylate cyclase activity and elevated cellular 3',5',cyclic-AMP (cAMP) content in a manner similar to AVP, indicating it is an agonist of VP action in renal tissue. These observations indicate that B-MLVP is an agonist of VP action and may be used to study renal VP receptors by employing avidin coupled to various reporter groups.