The proximal tubule is endowed with a variety of neutral amino acid transporters to ensure efficient reabsorption of this large group of metabolites. Molecular cloning efforts have successfully identified apical transporters for amino acids. The major transporter for neutral amino acids (SLC6A19 or B0AT1) mediates the uptake of all neutral amino acids. Mutations in this transporter cause Hartnup disorder. Surface expression of B0AT1 requires expression of collectrin (TMEM27) in the kidney or of angiotensin converting enzyme 2 in the intestine. Complete reabsorption of proline and glycine requires additional transporters, namely SLC6A20 (SIT1) and SLC36A2 (PAT2). Mutations in these transporters cause iminoglycinuria and glycinuria, two benign aminoacidurias, which are however interesting from a genetic point of view. Combination of different alleles can cause similar phenotypes in homozygotes, but present differently in heterozygotes. In mice neutral amino acid reabsorption is different from humans making use of SLC6A18 (B0AT3) instead of PAT2. Human SLC6A18 is an inactive protein, which is still expressed in the proximal tubule but does not appear to have a functional role. B0AT3 also requires collectrin or ACE2 for surface expression, but its expression mainly overlaps with collectrin. A mouse model lacking SLC6A19 in the intestine and kidney shows reduced body weight and cannot control body weight on diets of different protein content. On a high-fat diet the animals gain less weight than wild-type litter mates. Insulin sensitivity and glucose tolerance are improved compared to wildtype mice. The mechanisms underlying these physiological changes are currently under investigation.