Spontaneous vasomotor activity, as evidenced by the presence of alpha or beta waves in the paw plethysmogram, was demonstrated in 10 sympathectomized, 4 denervated, and 8 (ganglionic or adrenergic) blockaded extremities in dogs. Alpha waves occur during natural sleep and during anesthesia. They are present after removal and denervation of the carotid and aortic chemoreceptors. They occur in the splenectoinized animal. Alpha waves are usually synchronous in a pair of normally innerverted extremities. They may be synchronous, asynchronous, or absent in one paw when one extremity (or both) is denervated or sympathectomized. The significance of this information is discussed in relation to the factors which may control spontaneous vasomotor activity.