1. Experiments were carried out on two groups of anaesthetized greyhounds. The response of the first group to infusions of angiotensin II into a vertebral artery for 5 min and to bilateral occlusion of the common carotid arteries for 2 min was studied before and after bilateral ablation of the areas postrema. The response of the second group to infusions of angiotensin and to carotid occlusion was studied before and after mid-collicular transection of the midbrain.

2. Bilateral ablation of the areas postrema abolished the response to angiotensin infused into a vertebral artery at the dose used but did not significantly alter the response to carotid occlusion. Transection of the midbrain did not abolish the response to either procedure.

3. It is concluded that the structures involved in the cardiovascular response to carotid occlusion are anatomically distinct from the area postrema and that neither response requires the integrity of connections above the pons.

4. An attempt has been made to construct a schematic diagram of the vasomotor centre.

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