In the present paper we describe a new carboxylic acid transporter in Escherichia coli encoded by the gene yaaH. In contrast to what had been described for other YaaH family members, the E. coli transporter is highly specific for acetic acid (a monocarboxylate) and for succinic acid (a dicarboxylate), with affinity constants at pH 6.0 of 1.24 +/- 0.13 mM for acetic acid and 1.18 +/- 0.10 mM for succinic acid. In glucose-grown cells the Delta yaaH mutant is compromised for the uptake of both labelled acetic and succinic acids. YaaH, together with ActP, described previously as an acetate transporter, affect the use of acetic acid as sole carbon and energy source. Both genes have to be deleted simultaneously to abolish acetate transport. The uptake of acetate and succinate was restored when yaaH was expressed in trans in Delta yaaH Delta actP cells. We also demonstrate the critical role of YaaH amino acid residues Leu(131) and Ala(164) on the enhanced ability to transport lactate. Owing to its functional role in acetate and succinate uptake we propose its assignment as SatP: the Succinate-Acetate Transporter Protein.