To clarify the in vivo involvement of cellular adhesion molecules and cytokines in human glomerulonephritis, we have investigated the glomerular and interstitial expression of intercellular adhesion molecule 1 (ICAM-1) in 69 kidney biopsy specimens by immunohistochemical methods and its correlation with serum bioactive tumor necrosis factor alpha (TNF-α) and soluble ICAM-1 (sICAM-1) levels in 43 cases. In normal controls, glomerular ICAM-1 expression and serum TNF-α and sICAM-1 levels showed a mean score of 1.0 (n = 7) and were 12.1 ± 1.5 and 187 ± 5 ng/ml (mean ± SEM, n = 25), respectively. ICAM-1 was positive in 68 kidneys except in 1 patient with membranous nephropathy at various degrees in glomeruli and in 72% of peritubular capillaries or venules in the interstitium. Serum-bioactive TNF-α levels increased in the patients with IgA nephropathy, purpura nephritis, and lupus nephritis (LN) (18.9 ± 4.1, 32.6 ± 13.3, and 20.9 ± 3.5 pg/ml) and were positively correlated with the grade of glomerular ICAM-1 expression (n = 43, r = 0.57, p < 0.001), endocapillary proliferation with exudative lesions (r = 0.72, p < 0.001) and hematuria (r = 0.62, p < 0.001). Serum sICAM-1 levels were elevated in patients with LN and purpura nephritis and decreased from 312 ± 40 to 226 ± 21 ng/ml after methylprednisolone pulse therapy in LN (n = 9, p = 0.0285). sICAM-1 levels were positively correlated with the grade of interstitial ICAM-1 expression (r = 0.46, p < 0.05), and sICAM-1 levels ( > 210 ng/ml) showed high odds ratios in the interstitial ICAM-1-positive cases and systemic vasculitides such as purpura nephritis and LN (6.00, p = 0.0355; 6.50, p = 0.0216, respectively). These results suggest that bioactive TNF-α might relate to glomerular ICAM-1 expression associated with endocapillary lesions in human glomerulonephritis and that sICAM-1 levels may be used as a clinical marker to assess interstitial lesions in human nephritis and systemic vasculitides.