Abstract
Stereological techniques were applied to an electron microscopic study of biopsy samples from nine human lungs with diffuse pulmonary histiocytosis X, and the results were compared with values for normal lungs. This made possible a morphometric analysis of the tissue changes associated with the measurable abnormalities in gas transfer present in this disease. The small increases in arithmetic mean thickness of the alveolar-capillary membranes appeared insufficient to account for the reduction in gas transfer present. When compared with normal lung, a threefold increase in volumetric fraction of septal intercapillary tissue was found along with a corresponding decrease in septal capillaries. While uniformity of distribution cannot be determined by this method, it appears that abnormalities of blood gas transfer in this disease result primarily from a decrease in the available diffusing surface and the ventilation-perfusion distrubances with which these tissue changes are associated.