The current level of computed tomography (CT) scanner resolution is such that CT is possibly the best radiographic procedure available for viewing gross pulmonary anatomy and pathology. CT densitometry, in contrast, is of limited value in assessing diffuse lung disease because of partial volume errors created by the wide range of intrathoracic tissue densities. Anteroposterior density gradients and total mean lung density can be used advantageously in a select group of patients with suspected high-density disease. The morphologic patterns of diffuse high-density lung disease as viewed on conventional roentgenograms correlate closely with those depicted on CT images. Density measurements in normal and abnormal patients suggest that the medulla of the lung may be a reservoir zone that accommodates increased blood flow via distention and recruitment of vessels under appropriate conditions. Pulmonary diseases that cause oligemia can be identified and distinguished by their combined CT densitometric and morphologic characteristics. Combined high- and low-density disease may need total integration of plain radiographs, isotopic scans, and CT scans for proper interpretation.