The electroencephalographic results of a trial with an ergot alkaloid preparation (Hydergine) and placebo in 39 patients presenting cerebrovascular insufficiency, selected by rigid criteria and presenting good physical conditions, no past history of cerebro-vascular accident, Parkinson's disease and without psychotic senile disturbances are reported. Apart from slight changes in blood pressure, no significant clinical effects were observed. The 39 patients (average age 59,8 yearss) received Hydergine and placebo by intravenous injection in alternating days according to a randomization schedule in double-blind cross-over conditions. Statistically significant improvements were noted in the EEG alterations in this group of senile patients during the first and second hours after the administration of the active drug against the administration of the placebo. The correlation between the action of Hydergine and the cerebral bioelectrical activity is discussed.