The orphan transporter XT2 belongs to the SLC6 family and exhibits a high level of identity to B0AT1 (50-52%), the Na+ cotransporter of neutral amino acids causative of most cases of Hartnup disorder. As yet no data directly demonstrating the function of XT2 have been reported. We have detected high levels of XT2 mRNA and protein in mouse kidney, by RT-PCR and Western Blot, respectively. Using immunofluorescence, we showed that XT2 localizes to the apical brush border membrane of the later proximal tubule segments (S2 & S3), complementary to B0AT1, which mostly localises to the early proximal tubule (S1). In the original description by Quan et al., XT2-/- mice were shown to present a major urinary loss of glycine and a surprising elevation of blood pressure. Our new investigations of XT2-/- mice confirm their important urinary loss of glycine and other neutral amino acids. Telemetric measurements show a significant stress induced increase in blood pressure and respiratory rate suggesting a dysregulation of the autonomous nervous system. In summary, the structural similarity of XT2 to B0AT1, its complementary localization in kidney proximal tubule and the aminoaciduria of the XT2-/- mouse suggest that XT2 exerts an amino acid transporter function that is comparable and complementary to that of B0AT1. Further investigations will aim at elucidating the mechanism by which XT2 loss leads to stress- sensitivity of blood pressure and respiratory rate.