Circulating intercellular adhesion molecule-1 (ICAM-1) levels were measured in 48 patients with atopic dermatitis (mild in 29, moderate in 13, and severe in 6) and in 32 controls. Circulating ICAM-1 levels gradually increased with the severity of atopic dermatitis (216 +/- 68 in control, 323 +/- 66 in mild, 376 +/- 92 in moderate, and 555 +/- 93 ng/mL in severe atopic dermatitis, respectively). A significant correlation was observed between serum ICAM-1 and eosinophilic cationic protein levels in patients with atopic dermatitis (r = .71, P < .01). Although a significant positive correlation was observed between serum eosinophilic cationic protein levels and peripheral eosinophil counts (r = .63, P < .01), only a weak correlation was observed between serum ICAM-1 levels and peripheral eosinophil counts (r = .35, P < .05). Changes in serum ICAM-1 levels in ten patients treated with ketotifen for 3 months were also demonstrated A close correlation was observed between serum ICAM-1 levels and the disease severity (r = .76, P < .01. From these results, we speculate that serum ICAM-1 level may reflect the extent of inflamed tissue in atopic dermatitis.