The volume densities and dimensions of tubular bodies (Weibel-Palade bodies) in dog pulmonary capillary endothelial cells were examined by means of stratified random sampling and electron microscopic morphometry. The mean volume density of tubular bodies in normal (control) lungs was 0.43 ± 0.29%. The mean volume densities of tubular bodies in stable, isolated lungs perfused for 1/2 hour, 1 hour, and 2 hours and in lungs made edematous by increasing hydrostatic pressure or by decreasing oncotic pressure did not vary significantly from that of normal lungs. The mean thickness of the endothelium measured at the middle of the tubular bodies of normal dog lungs was nearly twice the mean thickness of the overall capillary endothelial cell sample. The mean endothelial thickness across tubular bodies from stable and from edematous isolated perfused lungs did not differ significantly from that of the control group. The mean width of tubular bodies from normal dog lungs was 0.25 ± 0.06 μm and the mean length was 0.81 ± 0.61 μm. The mean widths and lengths of tubular bodies from stable and from edematous isolated perfused dog lung endothelial cells did not differ statistically from those of normal dog lungs. Thirty percent of the tubular bodies in the sample were found to be adjacent to a mitochondrion in the same plane of section. Tubular bodies contained both tightly packed and loosely grouped tubules. It is concluded that the tubular bodies in canine pulmonary endothelial cells remain stable during the perfusion of isolated lungs and in oncotic and hydrostatic edema of isolated perfused lungs.