The application of the calorimetric detection seems to be an interesting possibility for the determination of single substrate components in mixtures or for the identification of substrate systems. The flow injection technique is used for a sequential initialisation of different enzyme catalysed reactions. The method is developed by use of a conventional flow-through calorimeter and demonstrated for a ternary system containing glucose, urea and penicillin G. More effective working conditions are realised by application of our IC calorimeters. First results from investigations with a flow-through IC calorimeter are communicated.