1. The effects of bradykinin (1-5 mug) injected into the cannulated lateral cerebral ventricles were studied in unanaesthetized rabbits before and after intravenous atropine, diphemanil and morphine.2. The intraventricular injections of bradykinin produced a short-lasting phase of behavioural excitation with vocalization followed by sedation. The behavioural excitation was associated with desynchronization in the electrocorticogram (e.co.g.), bradycardia and hypotension followed by tachycardia and hypertension. Tachypnoea was also observed. The subsequent phase of sedation was more prolonged and associated with synchronization of the e.co.g. and signs of catalepsy. Intense miosis was present during both phases.3. With repeated intraventricular injections of bradykinin, excitation, miosis, cardiovascular responses and tachypnoea diminished and eventually disappeared but the sedation did not exhibit tachyphylaxis.4. Atropine abolished the e.co.g. desynchronization, vocalization and bradycardia, reduced the duration of the excitatory and sedatory phase, diminished the tachycardia and hypotension, enhanced the hypertension, but did not affect the miosis and tachypnoea.5. Diphemanil affected only the cardiovascular effects produced by intraventricular bradykinin. They were affected in the same way as by atropine.6. Morphine did not affect the excitatory phase, but enhanced the cardiovascular effects produced by intraventricular bradykinin.7. The intraventricular injection of bradykinin (50 mug) caused a reduction in the amount of noradrenaline but not of 5-hydroxytryptamine (5-HT) in the brain stem; the amount of dopamine in the caudate nuclei was not affected.8. It is suggested that central cholinergic and adrenergic systems are activated by intraventricular bradykinin.