Creatine kinase is considered a key enzyme for the intracellular transport and storage of high energy phosphate in muscle, brain and heart, through the postulated creatin-creatine phosphate shuttle patway. The presence of creatine kinase has been reported in several solid and ascitic tumours. However, a mitochondrial creatine kinase activity has not been so far identified in tumours. In this work we reported the purification and some molecular properties of the citoplasmatic creatine kinase and a preliminary indication of the presence of creatine kinase activity in mitochondria isolated from Ehrlich carcinoma cells.[...]