Adrenaline and noradrenaline introduced into the third ventricle or cisterna magna of cats in total doses ranging from 50 μg to 3 mg produce wakefulness and excitation. The larger doses produced prolonged arousal (a minimum of 3 h, which was the longest time of observation), accompanied by excitation in the form of restlessness and an apparent compulsive need to be in continuous motion. With lower doses the initial excitation was less marked but could last from 20 to 30 min. This was at times followed by a mild form of sedation which, however, could not in any way be identified as sleep.