[en] Pulmonary function measurements during exercise were tested for accuracy and reproducibility in 5 saddle ponies weighing 267 +/- 9 Kg. Airflow (V) and tidal volume (VT) were measured with a Fleisch pneumotachograph mounted on a face mask. The linearity of the response and the symmetry of this device were carefully checked. Pleural pressure changes were measured by pleural puncture (Ppl) and with an esophageal balloon catheter (Pes). The elastance of the esophageal wall and the effect of the position of the esophageal catheter tip on Pes were also investigated. Airflow, VT, Ppl, Pes, mask pressure, an electrocardiogram and limb movements were simultaneously recorded before, during and after exercise. These recordings were used to assess the validity of some pulmonary function measurements and to evaluate the influence of the breathing apparatus on the respiratory pattern. Maximal intrathoracic pressure changes and total pulmonary resistance values did not differ significantly when calculated on the basis of the Ppl and the Pes curves respectively. Although the absolute Ppl values were significantly different from the absolute Pes values, both pressures recorded at different workloads were closely correlated (R = 0.99). The mean specific elastance of the esophagus was 1.56 +/- 0.24 kPa.cm.ml.-1. Changes in the position of the esophageal catheter tip induced significant differences in the recorded Pes values. The pressure/flow relationship of the pneumotachograph pressure transducer system was linear within the range of the V measured during exercise. The mask had a significant influence on respiratory frequency and maximum difference in Pes, but did not modify the exercise-induced changes in these parameters. It was concluded that the technique and methods used in this study can allow accurate pulmonary function measurements in exercising ponies.