The ability of computed tomography to visualize the normal pretracheal retrocaval (PTRC) space and its contents, at the level of the azygous arch, was investigated in 127 normal subjects. The scan level which shows the azygous vein entering the posterior aspect of the superior vena cava was analyzed. The perimeter of the PTRC space could be accurately delineated by following the trachea, azygous arch, superior vena cava, and aorta. The size, density, and contents of the PTRC space were measured. The surface area of the PTRC space increases significantly with the degree of mediastinal adiposity (p less than 0.0001), age (p less than 0.0001), and aortic unfolding (p less than 0.001). The mean density of the PTRC space was negative in the majority of subjects but varied from -107 to +48 H. Normal lymph nodes (azygous nodes) were detected in 88.1% of subjects. More than one lymph node was present in 29.9% of subjects. Three nodes were visible in each of nine subjects. There were 160 lymph nodes with a diameter of 5.5 +/- 2.8 mm visable in the 127 subjects. Eleven nodes were larger than 10 mm. Normal azygous lymph nodes can be visualized and subtle enlargement of these nodes detected.