The creatine⁄creatine kinase system decreases drastically in sarcoma. In the present study, an investigation of catalytic activities, western blot and mRNA expression unambiguously demonstrates the prominent expression of the creatine-synthesizing enzymesl-arginine:glycine amidinotransferase andN-guanidinoacetate methyltransferase in sarcoma, Ehrlich ascites carci-noma and Sarcoma 180 cells, whereas both enzymes were virtually unde-tectable in normal muscle.