A gene (ansP), which encodes an L-asparagine permease, has been isolated from a cosmid library of Salmonella enterica during screening for recombinant clones which encode L-asparaginase. Nucleotide sequence analysis reveals that the gene product is a polypeptide of 497 amino acid residues, containing 12 putative transmembrane segments. The calculated molecular mass is 54 kDa, although maxicell analysis by SDS-PAGE gave an apparent molecular mass of 37 kDa. Comparison of the deduced amino acid sequence with sequence databases showed significant homology with a family of basic and aromatic amino acid permeases. Strains containing the cloned ansP gene demonstrated a many-fold increase in L-asparagine uptake in comparison with control strains.