Fluorescence intensity of thioflavin T fluorogenic label increased significantly as a result of formation of enzyme-inhibitory complex with acetylcholinesterase of human blood erythrocytes. Thioflavin T is a reversible inhibitor, selectively reacting with acetylcholinesterase. Thioflavin T fluorescence intensity is proportional to acetylcholinesterase activity for the studied interval of enzyme activities. A rapid fluorescent method for measuring acetylcholinesterase activity is proposed.