Twenty hospitalized patients have been treated for acute mania with doses of 450-750 micrograms/day of clonidine (an alpha 2-adrenergic agonist), for one month. The tolerance to the given doses was excellent. A marked decrease of the manic symptoms was noted in 65% of the patients during the first 10 days of the treatment. The response was prompt and maintained for the whole period of the research, the clonidine being efficient on the whole scale of the manic syndrome. The sedating effect was much lower than in the case of neuroleptics; it is quite likely that the clonidine could represent an advance in the acute treatment of manic patients.