1. A series of veratrum alkaloids including two new ones, germitrine and neo-germitrine, which have recently become available have been studied for their effect upon the circulation of dogs. 2. Germitrine and neogermitrine, as well as other veratrum alkaloids, produce reflex respiratory and circulatory effects. In major part these responses are initiated by stimulation of afferent fibers which run in the vagiaortic nerves. 3. All clinically active veratrum alkaloids produce a reversible blockade of the carotid sinus pressor reflex. Activity upon this particular reflex corresponds approximately to the reported therapeutic action of these agents in hypertension. It is suggested that this may be made the basis of bioassay procedures for this group of substances. 4. Results are suggestive that an important action of the veratrum alkaloids may be directly on the vasomotor center. 5. In excessive doSAGE, germitrine and neogermitrine produce a rise in blood pressure rather than a fall. © 1952, SAGE Publications. All rights reserved.