Tian-Calvet conduction microcalorimetry has been applied to aldolase quantitation via measurement of fructose phosphate degradation. The endothermic reaction response measured from net chart deflection was directly proportional to enzyme levels at a constant-excess concentration of fructose phosphate. There was no significant interference in determinations of aldolase as added to human serum. Enthalpic measures for the fructose monophosphate reaction were significantly less than those for fructose diphosphate and aldolase. The simplicity of analysis, capability for monitoring aldolase substrate affinity and measurement in biological fluids suggest considerable potential including clinical isoenzyme determination.