The quantitative distribution of blood vessels in the barrel region of somatosensory cortex of the rat was studied to determine the relationship of the vascular pattern to a functionally specialized cortical structure. Blood vessels were found to arborize in layers III and IV and to decrease in number toward layers I and VI, creating a spindle-shaped pattern through the cortex. The density of blood vessels was greater in the barrel core versus septal regions of layer IV. The distribution pattern of blood vessels within the barrel region was remarkably non-random and constant even between animals. The pattern was consistent enough to form a reliable set of landmarks with which to identify a specific barrel from light- to electron-microscopy transition.