In vitro tumor necrosis factor-alpha (TNF-alpha) production from peripheral blood monocytes (PBMC) was investigated among 12 patients (male: 7, female: 5) with uveoretinitis of Behçet's disease and 6 age-matched healthy controls. TNF-alpha production of PBMC after the stimulation with lipopolysaccharides (LPS) was significantly enhanced in Behçet's disease patients with active uveoretinitis (21.5 +/- 2.8 U/ml) compared with both controls (5.7 +/- 1.8 U/ml) (p < 0.01) and inactive cases (5.1 +/- 1.4 U/ml) (p < 0.01). In the cases with active uveoretinitis, TNF-alpha production in the period of ocular attack (7.2 +/- 6.2 U/ml) was significantly lower than that of the post-attack period (24.4 +/- 13.9 U/ml) (p < 0.02). These results may indicate that TNF-alpha plays an important role in the immunopathogenesis of uveoretinitis in Behçet's disease.