Blood pressure regulation is compromised in persons with tetraplegia due to de-centralization of sympathetic cardiovascular control, associated with hypotension during upright positioning (7, 10, 18, 33). An alpha receptor agonist (midodrine hydrochloride) has been reported to raise blood pressure in persons with tetraplegia (25, 26, 30). Midodrine is the only drug that is presently available to treat orthostatic hypotension. In the clinical armamentarium, it is always beneficial to have agents from multiple drug classes to treat a condition. In the treatment of hypertension, several classes of drugs may be prescribed to lower blood pressure, alone or in combination. The clinician and patient would benefit if another class of drug, with a totally separate mechanism of action, were available to treat orthostatic hypotension. A nitric oxide synthase inhibitor (NOSi), nitro-L-arginine methyl ester (L-NAME), has been shown by our group to "normalize" blood pressure in persons with tetraplegia (32). The safety and efficacy of these two hypertensive agents has not been investigated or compared in persons with chronic tetraplegia. Although the mechanism of action of each of these agents is appreciated, the relative cardiovascular effect in persons with SCI compared with controls is not known. The study will determine the efficacy and safety of these two medications at restoring mean arterial pressure (MAP) during daily activities in persons with chronic tetraplegia. Furthermore, the implication of restoring MAP to normal levels (80 10 mmHg) in individuals with tetraplegia on cardiovascular, autonomic, hormonal and cognitive function.