The objective of this study was to measure soluble intercellular adhesion molecule-1 (sICAM-1) in patients with Behçet's disease (BD) and to analyse the relationship of sICAM-1 levels with clinical and some laboratory measures of disease activity. Forty patients with BD fulfilling the International Study Group Criteria for the diagnosis of BD and 20 healthy controls were studied. Twenty patients had active, and 20 patients had inactive disease. Serum sICAM-1 was determined by a sandwich ELISA. The mean (+/- SD) sICAM-1 level was significantly higher in the whole BD group (297.3 +/- 86.6 ng/ml) than in the healthy controls (213 +/- 83.5 ng/ml; P < 0.05). The mean sICAM-1 levels in active and inactive BD patients were 315.7 +/- 76.3 ng/ml and 258.3 +/- 73.3 ng/ml, respectively. The mean sICAM-1 level in active patients was significantly higher than in inactive patients and healthy controls (P < 0.02 and P < 0.001, respectively). No statistically significant difference in mean sICAM-1 levels was found between inactive BD patients and healthy controls (P > 0.05). There was no statistically significant difference between the mean sICAM-1 levels of active patients with (351.3 +/- 77.2 ng/ml) or without vascular lesions (292 +/- 68.8; P > 0.05). In spite of a positive correlation between disease activity and both erythrocyte sedimentation rate and C-reactive protein (CRP; P < 0.01), we found no correlation between sICAM-1 and either of them (P > 0.05). The elevated levels of sICAM-1 may be due to endothelial cell activation and/or damage or may be the result of inflammation.(ABSTRACT TRUNCATED AT 250 WORDS)