ENZYMATICALLY REACTIVE SUBSTANCES CONTAINED IN AQUEOUS SOLUTIONS ARE QUANTITATIVELY DETERMINED BY INTRODUCING A DEFINED AMOUNT OF A SOLUTION SAMPLE CONTAINING THE SUBSTANCE TO BE DETERMINED AND WHICH IS FREE OF AIR BUBBLES, INTO A STREAM OF BUFFER SOLUTION IN A BLOCK-LIKE FASHION, WHEREIN THE BUFFER SOLUTION CONTAINS THE REAGENTS NECESSARY FOR AN ENZYMATIC REACTION WITH SAID SUBSTANCES AND FLOWS WITH CONSTANT VELOCITY AND WHEREIN THE INTRODUCTION OF THE BLOCK SAMPLE DOES NOT SUBSTANTIALLY ALTER THE VELOCITY OF FLOW, CONTACTING THE RESULTING STREAM WITH THE APPROPRIATE ENZYME AND THEN PASSING THE STREAM OVER A DETECTOR TO INDICATE THE AMOUNT OF REACTION HAVING OCCURED, AND RELATING READINGS FROM THE DETECTOR TO THE AMOUNT OF THE SUBSTANCE TO BE DETERMINED CONTAINED IN THE SAMPLE.