To evaluate the role of nitric oxide (NO) in ocular inflammation, tear nitrite and nitrates (NN) as NO end products were determined in 11 patients with Behcet's disease (BD) and in 11 with non-Behcet's uveitis (NBU) during the active and remission stages and in 12 healthy controls. Median (with the range) NN levels were 82.29 (59.60-98.25) mu mol/l in the active and 98.25 (52.88-246.92) mu mol/l in the remission stage of ED; 88.17 (25.99-116.73) mu mol/l in the active and 83.00 (31.04-250.28) mu mol/l in the remission stage of NBU and 109.17 (88.17-158.74) mu mol/l in the controls. The NN levels in the active stage of ED and NBU were significantly decreased when compared to the controls (p < 0.05; Kruskal-Wallis test). Decreased NN levels at the activation stage may be caused by the rapid transformation of the NO to peroxynitrites, which are highly oxidizing and cytotoxic substances. Copyright (C) 2001 S. Karger AG, Basel.