Pressures were recorded simultaneously from two apical and two basal sites in the potential pleural space and from the esophagus in five anesthetized dogs studied without thoracotomy while supported in the vertical (upright) position. Pressures were also recorded during stepwise withdrawals of one of the pleural catheters from the apex downward to levels below the base of the heart and of the esophageal catheter from diaphragmatic up to apical regions of the thorax. Closely similar gradients in end-expiratory pleural and esophageal pressures with vertical height in the thorax were obtained. At levels below the superior border of the heart, these gradients were close to 1 cm H2O/cm while considerably lesser gradients (average, 0.35 cm H2O/cm) were recorded above this level. However, the intraesophageal pressure was more positive than the corresponding intrapleural pressure interpolated to the same vertical height in the thorax (average difference, 4.5 cm H2O). Differences in vertical pressure gradients in different regions in the thorax are believed to be related to differences in average specific gravity of the structures occupying these respective thoracic regions.