The dibasic amino acid, L-arginine, is a substrate for both nitric oxide synthase (NOS) and arginase and therefore, plays an important role in cell signaling and cell growth. We examined the effects of various NOS inhibitors on L-arginine transport into rat renal brush border membrane (BBM) vesicles. L-Arginine uptake was stimulated in the presence of an inwardly directed Na+ gradient and an imposed inside negative potential in BBM but not basolateral membrane vesicles. In BBM vesicles, the L-arginine analogs, N-iminoethyl-L-orinithine and Nw-monomethyl-L-arginine (L-NMMA) were potent inhibitors of L-arginine uptake (IC50 of 0.48 and 0.82 mM, respectively), while Nw-nitro-L-arginine was less active (IC50 = 10 mM) and Nw-nitro-L-arginine methyl ester (L-NAME) was inactive. The inhibition of L-arginine transport by L-NMMA was competitive in nature. L-NIO, L-NMMA as well as L-arginine and L-lysine but not Nw-nitro-L-arginine methyl ester, trans-stimulated L-arginine uptake when preloaded into BBM vesicles. The L-arginine analogs had no effect on the transport of the neutral amino acid, L-leucine, in the same preparations. The data suggest that in addition to inhibiting NOS, the L-arginine analogs, N-iminoethyl-L-orinithine, L-NMMA and to a lesser extent L-NA, also inhibit L-arginine transport across the BBM of proximal tubules.