PEPT1 is an electrogenic apical transporter belonging to the SLC15A1 family. It is composed of 12 transmembrane domain (TMD) with a large loop between TMD9 and TMD10, and it shows a 60 % sequence homology with the corresponding mammalian protein. In addition to the absorption of di- and tri-peptides, it is also able to translocate other substrates as peptidomimetics drugs and ACE inhibitors, suggesting a possible role in intestinal drugs absorption. Complementary RNA of PEPT1, derived from the intestine of the sea bass Dicentrarchus labrax, was injected in Xenopus oocytes that were subsequently tested with electrophysiological techniques after 3-5 days after injection. Transport-associated currents were observed when these oocytes were exposed to extracellular solutions with different pH values (6.5, 7.0, 7.5, 8.0), in presence of various dipeptides (Gly-Gln, Gly-Sar, Ala-Ala) or tripeptides (Leu-Gly-Gly, Gly-Gly-Gly) at concentrations ranging between 0.1 and 10 mM. No currents were generated by histidine nor by other single amino acids or tetrapeptides (Gly-Gly-Gly-Gly). Sea bass PepT1 also exhibited presteady-state currents in the absence of substrates. Acidic pH slowed down the relaxation time constant of these currents and shifted both Q/V and t/V relationships towards more positive voltages. Michaelis-Menten analysis of the transport currents showed an increase in apparent substrate affinity at acidic pH, which was very similar to that exhibited by the related transporter from zebrafish (Danio rerio), but in contrast, did not demonstrate a significant effect of pH on the maximal transport current.