To study the local and systemic behavior of the tumor necrosis factor-alpha (TNF-alpha) in patients with active uveitis. TNF-alpha levels were measured in aqueous humor and peripheral blood samples using an enzyme-linked immunosorbent assay from 23 patients with uveitis and 16 control patients who had been operated on for uncomplicated cataracts. Aqueous humor and sera of patients with uveitis showed higher levels of TNF-alpha than those of controls (p < 0.001). A comparison of cytokine levels between aqueous humor and sera showed significantly higher levels of TNF-alpha in serum than aqueous humor (p < 0.001). Correlation studies using the regression test for successive steps showed that serum TNF-alpha levels correlated with recurrent uveitis (r = 0.4150; p = 0.0489). TNF-alpha is a cytokine that participates actively in the pathogenesis of clinical uveitis. Our data emphasize the greater systemic than local participation of TNF-alpha. Finally, an elevated serum TNF-alpha seems to be associated with a recurrent pattern of uveitis.