IT IS NOT an uncommon occurrence in carotid angiography that after the first injection of contrast medium nonfilling or incomplete filling of the cerebral vascular tree is found. Thus, if the opaque medium is visible at all, only the internal carotid artery may be filled, while its terminal branches, that is, the middle and anterior cerebral arteries, cannot be visualized. This is true even though no major obstructions can be disclosed and the time of exposure remains unchanged. Repeated injections into the same artery, and injections into the opposite one, will usually result in an angiographic demonstration of the entire vascular tree. At times, however, partial filling will ensue even on repeated injections, resulting in a series of films apparently indicating a holding up of the contrast medium due to obliteration of the internal artery. Within the current year, however, five cases have come under our observation that may shed