A prospective study over 15 months in 100 elderly patients with signs of cerebro-vascular impairment demonstrated by psychometric testing that Hydergine (an ergot alkaloid preparation: 4.5 mg daily) compensated the signs of dementia, present in the placebo group, and in some patients actually brought about a significant improvement in mental activity. Similar compensatory effect was also demonstrable in cerebral haemodynamics: in the placebo group there was a progressive increase in cerebral circulation time, an expression of decreased cerebral blood flow, while with Hydergine cerebral circulation time was shortened and stabilized. Serial EEGs, obtained in parallel with psychometric and circulation time tests, demonstrated a marked increase in the 8-10 Hz pattern which corresponds to the physiological alpha activity in this age group. Furthermore, there was a diminished variability in performance in the tested frequency bands with Hydergine, the opposite tendency being obtained in the placebo group.