Arginine (ARG) is a basic non-essential amino acid well known to participate in physiological functions such as i) vascular tone homeostasis as contributing to the production of nitric oxide (NO) and ii) immune response control, through NO synthase (NOS) and Arginase enzymes, respectively. The Arginine (Arg) ELISA kit allows for the determination of Arg in serum and plasma samples working with a sample volume of 20μL. The kit is easy to implement and well suited for both preclinical and clinical studies.