The dynamic computed tomography (CT) study of the brain consists of the rapid intravenous injection of 49 ml of radiographic contrast material in 7 sec followed by serial 5 sec CT scans with interscan times of only 1 sec. The data from these scans can be reprocessed to create 12 segmented images in 35 sec. When small samples of four to six pixels of cortex are examined by the cursor, sharp rises of 20 to 25 CT units (500 scale) are seen on the time--density curves. Samples of white matter are usually no more than 2 CT units. When larger cursor samples of 220 to 255 pixels including cortex and white matter are examined, the time--density curves represent a combination of these two patterns. Comparison between symmetrical areas in the two hemispheres generally shows parallel curves in controls. The studies provide high resolution cerebral perfusion images. In ischemia secondary to ipsilateral carotid stenosis, there is depression of the up-slope and a depressed and late peak. Infarctions show a flat perfusion curve. Several patterns in brain tumors are illustrated. The study, simple to perform, adds significant perfusion information to the previously static CT examination of the brain.