The fundamental principles of operation of an Immobilized enzyme flow analyzer have been studied. In particular, models have been developed to explain the dependence of peak height, area, and half-width on sample concentration (0.1 to 2000 mM), sample volume (40-2500 μ), system flow rate (0.3-4.5 mL/min) and column size (0.4-0.9 mL). The system employed in this study Is an Improved high speed thermochemical analyzer based on the use of the enzyme urease which is Immobilized on porous glass by covalent attachment. A sample throughput of over 60 per hour can be achieved In small (0.5 mL) columns packed with approximately 1000 units of enzyme when operated at a flow rate of 2 mL/mln. In general, we find that the dependence of the peak height, area, and width upon sample volume, flow rate, and column configuration are analogous to the behavior of a concentration sensitive chromatographic detector.