The enzyme transglutaminase is able to modify proteins by catalyzing crosslinking reactions, deamidation and incorporation of amines. These possibilities of changing the structure of proteins have been the subject of an increasing number of papers during the last 10 years. This work has shown that the reaction is dependent on the source of transglutaminase as well as substrate and conformation of the substrate. Also parameters such as pH, temperature, concentration of substrate and enzyme, salt etc. have been discussed.