The epithelial sodium channel (ENaC) is believed to represent the rate-limiting step for sodium absorption in the renal collecting duct. Consequently, ENaC is a central effector affecting systemic blood volume and pressure. Sodium and water transport are dysregulated in diabetes mellitus. Peroxisome proliferator-activated receptor ␥ (PPAR␥) agonists are currently used in the treatment of type 2 diabetes, although their use remains limited by fluid retention. The effects of PPAR␥ agonists on ENaC activity remain controversial. Although PPAR␥ agonists were shown to stimulate ENaC-mediated renal salt absorption, probably via the serum-and glucocorticoid-regulated kinase 1, other studies reported that the PPAR␥ agonist-induced fluid retention is independent of ENaC activity. Here we confirmed that four chemically distinct PPAR␥ agonists [pioglitazone, rosiglitazone, troglitazone, and 15-deoxy-⌬ 12,14 -prostaglandin J 2 (PGJ 2 )] do not enhance Na ϩ transport in cultured renal collecting duct principal mpkCCD c14 cells, as assessed by shortcircuit current measurements. However, the PPAR␥ antagonist 2-chloro-5-nitro-N-4-pyridinyl-benzamide (T0070907), and to a lesser extent 2-chloro-5-nitrobenzanilide (GW9662), were found to decrease Na ϩ reabsorption across mpkCCD c14 cell layers. Furthermore, pretreatment of monolayers with T0070907 diminished the insulin-stimulated sodium transport. PPAR␥ agonist PGJ 2 did not enhance insulin-stimulated Na ϩ flux via ENaC. We also show that PPAR␥ enhances ENaC activity when all three subunits are reconstituted in Chinese hamster ovary (CHO) cells. GW9662 inhibits ENaC activity when ENaC subunits are coexpressed in CHO cells with PPAR␥. In contrast, rosiglitazone has no effect on ENaC activity. We conclude that PPAR␥ activity is important for maintaining basal and insulin-dependent transepithelial Na ϩ transport and ENaC activity.