Terlipressin, a synthetic, systemic vasoconstrictor with selective activity at vasopressin-1 (V 1) receptors, is a pro-drug for the endogenous/natural porcine hormone [Lys 8]-vasopressin (LVP). We investigated binding and receptor-mediated cellular activities of terlipressin, LVP, and endogenous human hormone [Arg 8]-vasopressin (AVP) at V 1 and vasopressin-2 (V 2) receptors. Cell membrane homogenates of Chinese hamster ovary cells expressing human V 1 and V 2 receptors were used in competitive binding assays to measure receptor-binding activity. These cells were used in functional assays to measure receptor-mediated cellular activity of terlipressin, LVP, and AVP. Binding was measured by [ 3H]AVP counts, and the activity was measured by fluorometric detection of intracellular calcium mobilization (V 1) and cyclic adenosine monophosphate (V 2). Binding potency at V 1 and V 2 was AVP>LVP>>terlipressin. LVP and terlipressin had approximately sixfold higher affinity for V 1 than for V 2. Cellular activity potency was also AVP>LVP>>terlipressin. Terlipressin was a partial agonist at V 1 and a full agonist at V 2; LVP was a full agonist at both V 1 and V 2. The in vivo response to terlipressin is likely due to the partial V 1 agonist activity of terlipressin and full V 1 agonist activity of its metabolite, LVP. These results provide supportive evidence for previous findings and further establish terlipressin pharmacology for vasopressin receptors.