The data presented indicate that glutamine remained stable when prepared in citrate or aqueous solution, stored at 4°C for at least 8 weeks or at room temperature for 3 to 4 weeks. Analyses of deproteinized plasma indicate that the glutamic acid concentrations were constant and stable for approximately 4 weeks. Plasma glutamine determinations were also quantitatively reproducible with time. These results would also suggest that with deproteinization of blood, the values obtained for glutamic acid are not due to glutamine breakdown but are true glutamic acid values.