Abstract Transglutaminase (TGA) activity in four human colorectal carcinoma cell lines of differing metastatic potential, and the effects of mild proteolysis on this activity, was investigated. Rank order of metastatic activity measured in nude mice (intrasplenic injection) was found to be LS174T > SW620 > WiDr > SW480. Rank orders of TGA activity were SW480 > WiDr > SW620 > LS174T. Proteolysis of cell lysates increased LS174T TGA activity 42-fold, SW620 2-fold without affecting WiDr or SW480 activity. Hence a negative association exists between metastatic potential and TGA activity in human colorectal carcinoma cells. Furthermore, a positive association exists between proteolytic activation of TGA and metastatic potential.