The orphan transporter XT2 belongs to the SLC6 family and exhibits high similarity to B⁰AT1, the Na⁺ cotransporter of neutral amino acids causative of most Hartnup disorder cases. As yet, no direct data demonstrating the function of XT2 have been reported. In particular, expression of XT2 in Xenopus oocytes and cultured mammalian cells failed to result in its surface expression. However, the study of XT2^-/-mice has suggested a possible role in amino acid transport and in blood pressure control. We have detected a high level of XT2 in the kidney, at the RNA level by real time RT-PCR and at the protein level by Western blotting. Using immunofluorescence, XT2 was shown to localize mainly in the later segments of the proximal tubule in the apical brush border membrane. This axial distribution suggests that XT2 exerts a complementary function to that of B⁰AT1, which is mostly localised to the early proximal tubule. Unlike previously shown by others for the rat ortholog ROSIT, mouse XT2 was not increased under high Na⁺ diet. Also during acidosis or alkalosis, levels of XT2 mRNA and protein remained stable. The similarity and the localisation of XT2 relatively to B⁰AT1 along the proximal tubule suggests a comparable but complementary functional role of these two transporters. In order to characterise more precisely the impact of the absence of XT2 on renal amino acid transport and blood pressure control, we are currently backcrossing XT2^-/-mice into C57BL/6J background.