Agents for the detection of substrates with hydrolase activity

In a process for the detection of hydrolase activity on an absorbent or swellable carrier by mixing (a) a hydrolase-containing sample with a hydrolase substrate which is cleavable by the hydrolase, with consumption of water, into a chromogenic compound and (b) an oxidation agent capable of oxidizing said chromogenic compound to effect a color change and then relating the resultant color change to hydrolase activity, the improvement which comprises employing as the hydrolase substrate at a pH of from 5 to 11, a compound of the formula ##STR14## wherein each of R.sup.1, R.sup.2 and R.sup.3 is C.sub.1 -C.sub.4 alkyl, or phenyl optionally substituted in the meta- or para- position by C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy or mono- or di-(C.sub.1 -C.sub.6)-alkylamino, or optionally substituted by an O--X group in which X is a glycosyl, phosphate or acyl moiety of a natural substrate of the corresponding glycosidase, phosphatase or esterase, with the proviso that one of R.sup.1, R.sup.2 and R.sup.3 is phenyl as set forth above which is substituted by a O--X group as set forth above and that another or both others of R.sup.1, R.sup.2 and R.sup.3 is phenyl as set forth above without an O--X group, whereby glycosidase activity is detected when X is the glycosyl moiety, phosphatase activity is detected when X is the phosphate moiety or esterase activity is detected when is the acyl moiety.