The authors have treated 20 patients hospitalized for acute manic disorders with 450-750 micrograms of clonidine per day for a period of one month. The tolerance to the drug was excellent. A marked decrease in manic symptoms was noted in 65% of the patients after the first ten days of therapy. The response was rapid and was maintained for the entire duration of the study, and clonidine was efficient for all the symptoms of the manic syndrome. The supra-sedation effect was much lower than with neuroleptics, and clonidine could be considered to represent a practical progress in the acute therapy of manic patients. Clonidine, usually employed as an anti-hypertensive drug, is an alpha-2-adrenergic agonist. It is believed that this property decreases the neural transmission by noradrenaline by stimulating pre-synapsis inhibitor receptors.