1. Adult fowls (Gallus domesticus) with cannulae chronically implanted into the IIIrd cerebral ventricle and various other sites of the brain received microinfusions or injections of catecholamines, adenosine, 3',5'-cyclic AMP or its dibutyryl derivative. The effects of these substances on behaviour, electrocortical activity and body temperature were studied.2. Behavioural and electrocortical sleep with fall in body temperature were obtained with intraventricular noradrenaline, alpha-methylnoradrenaline and isoprenaline; dopamine was ineffective. The doses required to elicit sleep were smaller than those affecting body temperature. Following mebanazine, the effects of noradrenaline were prolonged and doses of dopamine, previously ineffective, lowered body temperature and induced behavioural and electrocortical sleep.3. Noradrenaline, alpha-methylnoradrenaline, isoprenaline and dopamine infused into the hypothalamus induced sleep and lowered body temperature. Effective doses of noradrenaline, alpha-methylnoradrenaline and isoprenaline infused into the hypothalamus were one-twentieth to one-fifth those for intraventricular injection. Tachypnoea developed with isoprenaline and dopamine. Additionally with dopamine, there was deviation of the head to the contralateral side, together with repetitive jerking movements of the head. These effects were prolonged and intensified by mebanazine, whereas the involuntary movements with dopamine were greatly reduced by haloperidol.4. Involuntary movements, but without sleep, were induced by infusing dopamine into the paleostriatum augmentatum; noradrenaline infused into this site was ineffective.5. In three of five fowls pretreated with aminophylline, 3',5'-cyclic AMP infused into the hypothalamus induced behavioural and electrocortical sleep; without aminophylline pretreatment, 3',5'-cyclic AMP was ineffective. Adenosine infused into the hypothalamus, following pretreatment of fowls with aminophylline, consistently induced behavioural and electrocortical sleep. Dibutyryl cyclic AMP infused into the hypothalamus of intact fowls elicited behavioural arousal, followed by bursts of electrocortical spikes (6 Hz) over both cerebral hemispheres, spikes subsequently becoming regular at 1 Hz. Clonic limb and body movements occasionally accompanied the bursts of spike activity, infrequently developing into convulsions. In fowl encéphale isolé preparations, in which dibutyryl cyclic AMP was infused into the hypothalamus, spike activity was confined to the ipsilateral hemisphere.