We present a rapid and sensitive flow injection method for the determination of arginine in dietary supplements. Detection was based on the chemiluminescence reaction of arginine with alkaline hypobromite. The response is proportional to analyte concentration over the calibration range, from 2.5 x 10(-6) to 1 x 10(-4) M, and a relative standard deviation of 1% was calculated (1 x 10(-5) M, n = 12). Samples required only aqueous dilution prior to analysis, and over 100 samples could be analysed per hour, which is superior to that achieved with conventional colorimetric and enzymatic procedures. The results obtained with the flow injection methodology were concordant with those achieved using high-performance liquid chromatography employing pre-column derivatisation and fluorescence detection.