In the renal collecting duct, vasopressin controls transport of water and solutes via regulation of membrane transporters such as aquaporin-2 (AQP2) and the epithelial urea transporter, UT-A. To discover proteins potentially involved in vasopressin action in rat kidney collecting ducts, membrane "raft" proteins were enriched by harvesting detergent-resistant membranes (DRMs) of the inner medullary collecting duct (IMCD) cells. Proteins were identified and quantified with LC-MS/MS. A total of 814 proteins were identified in the DRM fractions. Of these, 186 were enriched in the DRMs including several characteristic raft proteins. Immunoblotting confirmed DRM enrichment of representative proteins. Immunofluorescence confocal microscopy of rat IMCDs with antibodies to DRM proteins demonstrated heterogeneity of raft subdomains: MAL2 (apical region), RalA (predominant basolateral labeling), caveolin-2 (punctate labeling distributed throughout the cells), and flotillin-1 (discrete labeling of large intracellular structures). The DRM proteome included GPI-anchored, doubly acylated, singly acylated, chlolesterol-binding, and integral membrane proteins (IMPs). The IMPs were on average much smaller and more hydrophobic than IMPs identified in IMCD without DRM enrichment. The content of serine 256-phosphorylated AQP2 was greater in DRM than in non-DRM fractions. Vasopressin did not change the DRM-to-non-DRM ratio of most proteins, whether quantified by LC-MS/MS (n=22) or immunoblotting (n=6). However, Rab7 and annexin-2 showed small increases in the DRM fraction in response to vasopressin. In accord with the long-term goal of creating a systems level analysis of transport regulation, this study has identified a large number of membrane-associated proteins expressed in the IMCD that have potential roles in vasopressin action.