Repeated injections of angiographic contrast media led to disruption of the endothelial barrier of the cerebral parenchymal capillaries (blood-brain barrier) experimentally by (a) promoting pinocytosis and (b) opening the tight junctions which exist between the endothelial cells. Two mechanisms appear to be involved in this process. The hyperosmolar quality of the contrast media is responsible for the increased pinocytosis, while the chemical nature of the contrast agents used (Hypaque 50, and Conray 60), results in opening of the tight junctions.