SGLT1 mediates a part of glucose and galactose reabsorption in the mammalian proximal tubule (PT). Previous transport studies in isolated brush-border membranes (BBM) from various kidney regions, and hybridization studies in the kidney tissue from rats and rabbits, localized this transporter largely to the PT S3 segments in the outer stripe (OS) and medullary rays (MR). However, due to lack of good antibodies, the immunolocalization of SGLT1 along the mammalian nephron still awaits clarification. In this work we used a peptide-specific polyclonal antibody for rat SGLT1 (rSGLT1) and studied the transporter along the nephron of intact and variously-treated male (M) and female (F) rats by immunoblotting of BBM isolated from the kidney cortex (C) and OS, and by immunocytochemistry in tissue cryosections. These findings were correlated with the Na⁺-dependent, phlorizin-sensitive uptake of ³H-D-galactose in the BBM vesicles, tested by rapid filtration technique, and with the abundance of rSGLT1-specific mRNA in the C and OS tissue, determined by Northern blotting. In immunoblots of BBM from control animals, the antibody labeled two major protein bands; the abundance of a sharp, ~40 kDa band was not clearly zone- and gender-dependent, whereas the abundance of a broad, ~75 kDa band in both sexes exhibited strong zonal (OS > C) and gender differences (F > M). By immunocytochemistry, the antibody stained strongly brushborder in S3 in the OS and MR and smooth muscles of the blood vessels and renal capsule, and weakly the apical domain of other PT segments in the C. Strong gender differences (F > M) in the staining intensity were observed in S3 in the OS and MR, but not in the blood vessels. The phlorizin-sensitive uptake of ³H-D-galactose in BBM vesicles completely matched the immunoblotting data related to the 75 kDa band and the immunocytochemical data, thus proving zonal and gender differences in the functional transporter. Relevant gender differences (F > M) were also found for the rSGLT1-specific mRNA in the OS but not in the C. Ovariectomy had no effect, castration caused upregulation, whereas treatment of castrated rats with testosterone, but not with estradiol or progesterone, caused downregulation of the 75 kDa protein and the relevant immunostaining. The expression of the 40 kDa protein band remained unaffected by these treatments. We conclude that in the rat kidney, the expression of rSGLT1 is represented by 75 kDa protein localized largely in the PT S3 segments, where it exhibits gender differences (F > M) at both protein and mRNA level, that are caused by androgen inhibition.