Abstract: The effect of clonidine and some other amines on urinary flow were studied on rats and rabbits. Increase of urinary flow was observed after intraperitoneal (IP) administration of clonidine in rats.The diuretic action of clonidine was shown to be stroger than that of norepinephrine and methoxamine, and about fifty times stronger than that of hydrochlorothiazid in rats.The mechanism of diuretic action of clonidine may be due to its action on the central nervous system. Increase in urinary flow was also observed after ICV administration of clonidine (2,5 μg/rat), norepinephrine and methoxamine. The action was prevented by prior administration of α-adrenoceptor blocking agents (phentolamine, phenoxybenzamine, IVC or IP), but not by the histamine H₂-receptor blocking agent cimetidine (IVC). Decreased urine outflow was observed after IVC administration of isoprenaline.It appears that the mechanism of diuretic action of clonidine in rats is related to its stimulative action on the α-adrenergic receptors of the central nervous system.