The fibrinolytic activity of human brain was studied with the “fibrin slide technique” for the localisation of tissue plasminogen activators. The material consisted of brains obtained at autopsy of 25 adults without demonstrable intracranial disorders. Measured as the “focal lysis time” the fibrinolytic activity of gray as well as of white matter was found to be low and that of the leptomeninges high. The areas of lysis were situated along small blood vessels scattered over the section. This fibrinolytic activity was found to be localised to the advential layer of the vessel. The concentration of plasminogen activators in various parts of the brain was fairly uniform and relatively low. Major cerebral arteries, such as the internal carotid and basilar arteries, showed active centres of lysis in the intimal layer of the vessels. The ependymal cells lining the floor of the fourth ventricle showed very little or no activity. The choroid plexus was rich in plasminogen activators. One might imagine that large amounts of fibrinolytic activators in the leptomeninges may be released into the CSF after vascular damage and/or haemorrhage and thereby interfere with the first stages of vascular repair and premature dissolution of the clot formed after a haemorrhage.