We performed Ussing chamber experiments on cultured human bronchial epithelial cells to look for the presence of electrogenic dibasic amino acid transport. Apical but not basolaterall-arginine (10–1,000 μM) increased the short-circuit current. Maximal effect and EC₅₀ were ∼3.5 μA/cm² and 80 μM, respectively, in cells from normal subjects and cystic fibrosis patients. The involvement of nitric oxide was ruled out because a nitric oxide synthase inhibitor (N ^G-nitro-l-arginine methyl ester) did not decrease the arginine-dependent current. Apicall-lysine,l-alanine, andl-proline, but not aspartic acid, were also effective in increasing the short-circuit current, with EC₅₀ values ranging from 26 to 971 μM. Experiments performed with radiolabeled arginine demonstrated the presence of an Na⁺-dependent concentrative transporter on the apical membrane of bronchial cells. This transporter could be important in vivo to maintain a low amino acid concentration in the fluid covering the airway surface.