The concurrent concentrations of free amino acids in plasma, erythrocytes, lymphocytes, and granulocytes are investigated in healthy men. The concentrations of most amino acids, except for aspartic acid which is much higher in erythrocytes, are more or less similar in plasma and erythrocytes. In lymphocytes the levels of taurine and aspartic acid are 100 and 200 times higher than the plasma levels, respectively, while in granulocytes the levels of taurine and aspartic acid are 300 and 100 times higher than the plasma levels, respectively. Aspartic acid in blood cells may play an important role common to the formed compartments of the blood, while taurine may play important roles in functions peculiar to leukocytes, especially in granulocytes.This work was supported in part by a Grant-in-Aid for Scientific Research (Project NO. 544050) from the Ministry of Education, Science, and Culture of Japan
