The use of inhaled nitric oxide (NO) in research and clinical applications requires the monitoring of NO and its autooxidation product nitrogen dioxide (NO2) in inspired gas and in the ambient environment. We describe an inexpensive electrochemical NO and NO2 analyzer that uses a critical orifice constant-flow controller and a microprocessor crossover correction for the measurement of NO and NO2 in the concentration range relevant to the use of inhaled NO. The analyzer proved to have good accuracy and precision for NO and NO2 in the range of concentrations relevant to studies of inhaled NO. In this range, the performance was similar to that of a chemiluminescence analyzer, and the response characteristics were not affected by varying the O2 concentration of the mixtures analyzed.