The aim of the present study was to investigate a possible central monoaminergic influence on the control mechanism of the urinary bladder in rats. A selective central nervous stimulation was accomplished by injection of monoaminergic precursor (L-dopa and 5-HTP) after enzymatic blockade of its peripheral metabolisation. The bladder response was recorded with a cytometric procedure. The central adrenergic stimulation with L-dopa resulted in a hyperactive bladder response, with higher intravesical pressure and more prominent detrusor contractions than in control rats. Injection of 5-HTP had no such effect. The hyperactive bladder response to L-dopa was abolished by prior administration of a central dopamine receptor blocking agent (spiroperiodol). This indicated that the central effect on the bladder was elicited by dopaminergic structures. Peripheral adrenergic stimulation with metabolites of L-dopa--dopamine and noradrenaline--gave no measurable bladder response. The study showed that activation of central adrenergic mechanisms influenced urinary bladder control, i.e. evoked a hyperactive bladder response.