To understand the regulation of vasopressin receptors in an animal model of hypertension, localization and age-related changes in renal arginine vasopressin (AVP) receptors in spontaneously hypertensive rats (SHR) were investigated using in vitro (macro) autoradiography and a radiolabeled receptor assay. Autoradiography localized renal AVP V2 receptors to the distal tubules and collecting ducts in the medulla. We also found small numbers of AVP-binding sites within glomeruli, possibly representing VI receptors in the mesangium. The radiolabeled receptor assay of the medulla membrane fraction revealed that the binding affinity of renal V2 receptors did not differ significantly between SHR and control Wistar-Kyoto rats in any age group. However, the binding capacity (B<sub>max</sub>) for V2 receptors in 12-week-old SHR was significantly increased (p < 0.025) as compared with that of age-matched control rats. The B<sub>max</sub> values for V2 receptors in 3- and 7-week-old SHR were not significantly different from those of age-matched controls. There was no significant change in urine volume between SHR and control rats at the age of 12 weeks. The mean plasma AVP concentration in SHR increased at 7 and 12 weeks of age. These findings suggest that SHR have different developmental changes in kidney AVP receptors and that renal V2 receptors play a role in maintaining fluid homeostasis in SHR with established hypertension.