a method and apparatuses for determining the total content of proteases by means of measuring their enzyme activity after previous deinhibition is disclosed . in biological samples , lysosomal proteases are completely or partly inhibited . a method proposed for the deinhibition entails immersing a solid support material as plastic strip to which is linked , covalently or by adsorption , an inhibitor - binding substance which binds the inhibitor corresponding to the protease more strongly than the protease in the sample for measurement . after the deinhibition has taken place , the plastic strip is removed from the liquid sample for measurement , and the sample for measurement is passed on for measurement of the enzyme activity . fluorogenic substrates from which the fluorogen 7 - amino - 4 - trifluoromethylcoumarin is eliminated proved to be particularly advantageous for the activity measurement . these substrates make it possible for the sensitivity on measurement in microtitre plates with a fluorescence reader to be at least 10 times higher compared with conventional amc substrates in blood serum , and thus for the fluorimetric determination of such enzyme activities in blood serum to be efficient with this measuring arrangement which is widely used in clinical laboratories .