The breath-to-breath determination of total respiratory ozone (O3) uptake requires the monitoring of O3 concentration at the airway opening with an instrument that responds rapidly relative to the frequency of respiration. Originally, the authors developed an analyzer that used the homogeneous chemiluminescent reaction of O3 with 2-methyl-2-butene, but it was suitable only for monitoring O3 during quiet breathing and light exercise (Ben-Jebria and Ultman, Rev Sci Instrum 1989; 60:3004-11, and Ben-Jebria et al., Rev Sci Instrum 1990; 61:3435-39). The improvement of performance characteristics of the aforementioned analyzer enabled the authors to use the newly constructed and self-contained instrument, which used ethylene as the reactant gas, for respiratory O3 monitoring during moderate-to-heavy exercise. Operating at a reaction chamber pressure of 350 torr, an ethylene/sample flow ratio of 4:1, and a sampling flow of 0.6 lpm, the authors achieved an optimum analyzer performance (i.e., 10-90% step-response of 70 msec and a minimum resolution of 0.006 ppm O3). Furthermore, the new instrument did not exhibit the nonlinear calibration and the CO2 interference suffered by the original analyzer. To demonstrate the quality of the new O3 analyzer in a respiratory application (i.e., total O3 uptake), the authors measured a series of single breaths on two subjects who breathed 0.11 and 0.43 ppm O3-in-air mixtures for 15 min during rest, and during moderate and heavy exercise.