We investigated which of the NaCl transporters are involved in the maintenance of salt sensitive hypertension. Milan hypertensive (MHS) rats were studied 3 months after birth. In MHS, as compared to normotensive strain (MNS), mRNA abundance, quantified by competitive PCR on isolated tubules, was unchanged both for Na⁺-H⁺ isoform 3 (NHE3) and Na⁺-K⁺-2Cl^- (NKCC2), but higher (119%, n=5, p<0.005) for Na⁺-Cl^- (NCC) in distal convoluted tubules (DCT). These results were confirmed by Western blots which revealed: 1. unchanged NHE3 in the cortex and NKCC2 in the outer medulla; 2. a significant increase (52%, n=6, p<0.001) of NCC in the cortex; 3. - and -sodium channels (ENaC) unaffected in renal cortex and slightly reduced in the outer medulla, while -ENaC remained unchanged. Pendrin protein expression was unaffected. The role of NCC was reinforced by immunocytochemical studies showing increased NCC on the apical membrane of DCT cells of MHS animals, and by clearance experiments demonstrating a larger sensitivity (p<0.001) to bendroflumethiazide in MHS rats. ClC-K chloride channels were studied by western blot experiments on renal cortex and by patch-clamp studies on primary culture of DCT dissected from MNS and MHS animals . Electrophysiological characteristics of CLC-K channels were unchanged in MHS rats, but the number of active channels in a patch was 0.60±0.21 (n=35) in MNS rats and 2.17±0.59 (n=23) in MHS rats (p<0.05). The data indicate that, in salt sensitive hypertension, there is a strong up-regulation both of NCC and ClC-K along the DCT, which explains the persistence of hypertension.