Repeated pulmonary function testing was performed on six 4- to 6-week-old resting, nonanesthetized Holstein-Friesian calves (av weight 59 kg). Under study conditions, PaO2, PaCO2 and pH were 73.3 mm of Hg, 41.2 mm of Hg, and 7.42, respectively. Mean ventilatory values for the group were: minute ventilation, 13.1 L/min/m2., and respiratory rate, 27.3 breaths/minute. Measurements of pulmonary mechanics were performed while animals breathed spontaneously through a pneumotachygraph. Intrapleural pressure was estimated, using an esophageal balloon-catheter. Total pulmonary resistance was 3.1 cm of H2O/L/sec and dynamic pulmonary compliance was 0.15 L/cm of H2O. These values have not been reported previously in the calf but agreed well with predicted values derived from comparative studies in other species. Efficiency of intrapulmonary gas mixing was estimated, using a N2 washout technique, and results agreed favorably with values previously reported in the dog.