The intercellular adhesion molecule-1 (ICAM-1) is a membrane-bound molecule involved in cell-cell adhesive interactions which is upregulated on inflammatory epithelial cells. The levels of soluble ICAM-1 (sICAM-1) shed into the gingival crevicular fluid (GCF) were studied in healthy patients and patients with gingivitis, adult periodontitis or rapidly progressive periodontitis, using an ELISA technique. Clinical parameters including plaque index, gingival index, probing depth, and bleeding on probing were recorded following careful sampling of GCF with standardised filter strips. In GCF, sICAM-1 levels were higher for patients with plaque (p=0.04) and for patients with inflammation (p=0.02), but did not correlate with disease classifications. These results suggest that elevated GCF sICAM-1 levels may represent increased shedding of this molecule in the interstitial fluid as a result of membrane-bound ICAM-1 upregulation on ICAM-1 gingival-bearing cells in relation with plaque accumulation and inflammation.