For the assay of transcobalamin (Tc) I plus III in human serum a simplified method has deen developed which involves either acidification or adsorption by Quso G32. Tc II disappeared when pH of serum was decreased to 1.8 without any change of Tc I and III. Tc II was also adsorbed almost completely by Quso G32 without altering Tc I and III. These two techniques provide a simple and rapid means to determine Tc I plus III, known to be produced by and hence an indirect measure of granulocytes.