A flow enthalpimeter for use with two fluid streams has been designed. It is based on a related device for use with one fluid stream and a bed of catalyst. Satisfactory results were obtained only when the two thermistors, which comprise part of a differential temperature measurement system, are subjected to the same net flow. In addition, any volume located between the point of reagent mixing and the adiabatic column must be minimized. Assays for mineral acid, calcium ion, nitrite based upon their reaction with tris(hydroxymethyl)-aminomethane, ethylene bis(oxyethylenenitrilo)tetraacetic acid, sulfamic acid, respectively, have been developed. Detection limits ranged from 10 μM to 1 mM, depending upon the heat of reaction and achievable base-line stability. Sample volumes of 120 μL and a flow rate of 2.5 mL/min allow for a throughput of nearly 60 samples/h. In general, sample volume, concentration, flow rate affected the signal height and width in a fashion similar to that observed with an immobilized enzyme analyzer based on a related flow system. The chief differences in behavior occur at low sample concentration.