A METHOD FOR DETERMINING ENDOHYDROLASE WHICH BREAKS DOWN POLYSACHARIDE IN AN AQUIOUS SAMPLE WHICH COMPRISES CONTACTING THE SAMPLE WITH A REAGENT CONSISTING OF A WATER-INSOLUBLE BUT HYDROPHILIC, SWELLABLE, ENZYMATICALLY HYDROLYZABLE THREE-DIMENSIONAL NETWORK OF MOLECULES OF EITHER A POLSACCHARIDE OR AN ENZYMATICALLY HYDROLYZABLE DERIVATIVE OF A POLYSACCHARIDE. THE MOLECULES ARE CROSSLINKED WITH BONDS OF A COVALENT NATURE. ALSO THE THREE-DIMENSIONAL NETWORK PRESENTS INDICATABLE SUBSTITUENTS BOUND BY MEANS OF BONDS OF A COVALENT CHARACTER. THE CONTACTING CAUSES A REACTION TO TAKE PLACE BETWEEN THE ENZYME AND THE REAGENT WHEREBY WATER-SOLUBLE FRAGMENTS OF THE REAGENT CONTAINING INDICATABLE SUBSTITUENTS ARE RELEASED. THE UNDISSOLVED REAGENT IS SEPARATED FROM THE LIQUID WITH THE WATER-SOLUBLE FRAGMENTS OF THE REAGENT DISSOLVED THEREIN, AFTER THE ENZYME HAS ACTED UPON THE REAGENT FOR A DETERMINED PERIOD OF TIME. THE INDICATABLE SUBSTITUENTS ARE THEN DETERMINED IN AT LEAST ONE OF THE TWO PHASES CONSISTING OF THE LIQUID PHASE AND THE UNDISSOLVED REAGENT MATERIAL PHASE AS A MEASURE OF THE ENZYME ACTIVITY. ALSO, THE REAGENT FOR DETERMINING ENDOHYDROLASE IN PROVIDED.