Abstract: Cellobiose dehydrogenase activity (range 0.25 to 1 iu mL-1) is monitored by oxidation of cellobiose to cellobionolactone. The cellobiose substrate, the 2,6-dichlorophenolindophenol(I) reagent solution in Tris buffer (pH 7.5) and the gluconolactone(II) solution in acetate buffer are mixed before addition of the enzyme. After incubation at 50°C for 20 s the absorbance is measured at 605 nm. The decrease in absorbance is a measure of enzyme activity, because I is reduced to a colorless compound. The presence of II prevents reaction of any β-glucosidase. With a sample throughput of 120 h-1, the correlation coefficient between the flow and manual procedures is 0.96 (n = 40).