A significant discrepancy was noted in our laboratory between the total plasma carbon dioxide concentration measured by the Kodak Ektachem 700 and the bicarbonate concentration derived from the Corning 170 pH/Blood Gas analyser in an 8-day-old patient. The concentration of total carbon dioxide was 18 mmol/L while the derived bicarbonate was 13 mmol/L. The patient was eventually diagnosed as maple syrup urine disease. This finding led us to examine the effect of various organic acids on the measurement of carbon dioxide by the Ektachem 700. Several interfered significantly. Clinicians should be aware that when organic acid concentrations are increased, the Ektachem 700 total carbon dioxide result may be falsely raised.