In summary, multiple pathways of angiotensin production may exist in the blood vessel wall (Fig. 1), in addition to the well described renin--ACE enzymatic axis. It is not known whether these enzymatic pathways represent in vitro phenomena, or authentic in vivo alternate pathways which are activated only when the renin--ACE pathway is blocked, or whether they are operative at all times in the vessel wall. If these multiple pathways are functional, then the vascular angiotensin system may be very complicated, and may vary in different pathophysiological states. Future research in this area is likely to yield important and novel information on the in vivo pathways of production and function of vascular angiotensin.