The EnzChek™ cellulase substrate was developed for simple and rapid quantitation of cellulase. The assay can be completed in 30 minutes or less. Simply mix the enzyme with the EnxChek™ cellulase substrate working solution, incubate, and read the results using excitation/emission maxima ∼339/452 nm. In contrast to other more complex, multistep assays, the EnzChek™ cellulase substrate is perfect for use in a high-throughput environment. This fluorescence substrate is highly sensitive, with a detection limit as low as 40 μU/mL cellulase. It is also possible to use this substrate in a colorimetric assay, albeit with reduced sensitivity.