Abstract: In a FIAstar 5020 automatic analyzer. (Tecator) with motor-driven injector loop (60 µL), streams (2 mL min-1) of aqueous thionine violet solution (0.2 mg mL-1) and of EDTA solution (3 g in 100 mL of water, diluted to 200 mL with acetate buffer of pH 4.7) were combined and passed through a glass reaction coil (1 m x 2 mm) under a 250-W high-pressure Hg lamp to reduce the dyestuff to its leuco form. Sample solution [e.g., Cr2O72-, Fe(CN)63-, VO3-, S2O82- or Fe3+] was injected into the stream, and the absorbance was measured at 600 nm in a Corning 252 flow-through photometer with a Hellma 178.012 QS flow-through cell (10 mm; 18 µL). Up to 180 samples h-1 can be analyzed. The limit of detection is ~1 µM. As H2O2 reacts only at concentration. of >10 to 100 mM, the determination of, e.g., 10 µM-S2O82- is possible in a 150-fold excess of H2O2.