SummaryThe dihydrogenated substances derived from ergotoxine and its group have three main pharmacodynamic actions in animals : they depress the central vasomotor tone with consequent hypotension ; they depress the sino-carotid centers sensitive to blood pressure ; they act peripherically as an adeonosympathicolytic agent.By intravenous injection, hydergine (an equal mixture of 3 dihydrogenated alcaloids) is an hypotensive and bradycardia producing agent in man ; this effect is especially definite in cases of arterial hypertension. It produces an orthostatic hypotension, it depresses the hypertension due to epinephrine and the vasopressor effect of the«cold pressor test»(Hines). Attempts of treatment .by hydergine were made in 20 cases of hypertension of various degrees. After two to throe months of treatment 10 to 25 % decrease in blood pressure was observed in 16 out of 20 cases. The control figures of blood pressure were the mean of the lowest figures obtained by usual treatments Subjective symptoms were abolished in 80 % of these cases. No toxic manifestations were observed. A statistical analysis of the data obtained was made with Fisher’sttest; spontaneous changes of blood pressure were taken into account. The results were significative in 14 out of 20 patients, this means that hydergine has a hypotensive action in 70%of the studied cases and that in these the effect due to mere hazard was presumably absent. Study of the coefficients of variation, before and after treatment, shows in most cases a stabilization of the blood pressure duo to a decrease in the paroxysms of hypertension. A definite effect of hydergine on blood pressure was still observed two months after the end of the treatment in 7 outof 16 cases. Hydergine is not t)he ideal drug for the treatment of hypertension, but its use in the therapy of this disease is a definite progress on the usual treatments like sedatives or anti-spasmodics. Any possible effect of the latter has been taken into account in this study.