Arginases (EC 3.5.3.1) catalyze the divalent cation dependent hydrolysis of L-arginine to produce L-ornithine and urea, the final step of the urea cycle. While arginase I (or liver arginase) is cytosolic, and is the best characterized of the mammalian arginases, arginase II (or kidney arginase), is mitochondrial in location. Due to its generation of L-ornithine, arginase is involved in several important downstream metabolic pathways. Most importantly, the enzyme is crucially involved in various aspects of inflammation. Arginase has been shown to be either responsible for or to participate in, for example, inflammation-triggered immune dysfunction, tumour immune escape, fibrosis, immunosuppression and immunopathology of infectious diseases. Small-molecule arginase inhibitors are currently described as promising therapeutics for the treatment of several diseases, including allergic asthma, inflammatory bowel disease, ulcerative colitis, cardiovascular diseases (atherosclerosis and hypertension), diseases associated with pathogens (e.g., Helicobacter pylori, Trypanosoma cruzi, Leishmania, Mycobacterium tuberculosis and Salmonella), cancer and induced or spontaneous immune disorders.