Black diamond coated polypropylene flow cells have been used to produce a stopped flow batch microcalorimeter. The instrument is under complete computer control for sample insertion, data collection, and analysis. Several biochemical reactions are presently being explored using the instrument. These include clatherin assembly, tRNA-transferase reactions and ATCase reactions with various substrates. Protein concentrations of 10-6M can be used with only 50 Mul needed per reaction. Four experiments per hour can be run at this level of sensitivity. The significance of the project lies in the possibility of detecting new reaction pathways as revealed by the thermal reactions and in the ability to make basic thermodynamic measurements on biological reactions where no other detection system is available. In addition, the direct measurement of the reaction enthalpy is a much more precise method than the determination using the Van't Hoff method, i.e. measuring of the reaction equilibrium at different temperatures. When the Van't Hoff method is used, the range of temperature, 4 degrees C to 40 degrees C, is too small for an accurate determination of the enthalpy. Thus to predict the change in reaction equilibrium in, for example, drug metabolism, a direct calorimetric measurement is much to be preferred.