A novel flow enthalpimetric analyzer is described and its use demonstrated by an analysis in which glucose is determined by its hexokinase catalyzed phosphorylation reaction. The method depends on measurement of the temperature differential across a column packed with glass supported immobilized enzyme. Sample volumes of 120 μl can be used to obtain a calibration curve that is linear up to 25 mmol of glucose per liter. A precision (within day) of 5% is generally observed in the optimum concentration range where glucose is quantitatively phosphorylated. Results by the technique correlate reasonably with those by the o toluidine and the hexokinase/glucose 6 phosphate dehydrogenase methods: Other sugars - including fructose, glucosamin, and mannose - will interfere; galactose does not. The technique is amenable to both routine and emergency analyses.