Abstract: Chromogenic substrates of the formula A--O--B are described, in which A represents the radical in the ion A--O.sup.- of a compound A--OH, whose absorbance is measured photometrically after hydrolysis of A--O--B, while B is the radical in a compound B--OH which makes the compound specific for the reaction with a given enzyme, and where A--OH is a hydroxynitropyridine, a hydroxynitrobenzopyranone, a dibenzox(or thi)azine or a dibenzopyranone or a derivative thereof, and B is a sugar or sugar derivative, an amino acid or an oligopeptide or an inorganic acid.These compounds can be used for the detection and determination of hydrolases.