A potent, reversible inhibitor of rat liver arginase with a Ki value of 0.5 µM, which is 20-fold lower than the Ki of 10 µM observed for NOHA; about 40-fold more potent than NOHA as an inhibitor of arginase from mouse macrophages, exhibiting an IC50 of 10-12 µM; not a substrate for any of the 3 NOS isoforms; does not inhibit nNOS or iNOS.