Objective: To examine the influence of systemic nitric oxide (NO) synthesis on blood pressure in patients with chronic renal failure undergoing haemodialysis, since nitric oxides are susceptible to renal excretion or are dialysed, a different indicator that is unaffected by renal function, such as the level of exhaled NO was evaluated. We examined the levels of the endogenous NO before and after a haemodialysis session. Design and methods: We evaluated the serum concentrations of nitrite/nitrate and the rate of nitric oxide release into exhaled air in 10 patients with hypertension who were receiving maintenance haemodialysis. Results: The serum concentrations of nitrite/nitrate before haemodialysis were significantly higher than those in 10 normal controls (183 ؎ 151 M vs 42 ؎ 17 M, P Ͻ 0.05). These levels decreased signifi-