Inflammatory mediators such as interferon-gamma (IFN-gamma) are known to induce the expression of class II HLA (HLA-DR) and intercellular adhesion molecule 1 (ICAM-1) in a variety of cell types including epithelial cells. The coexpression of ICAM-1 and HLA-DR has been implicated in the pathogenesis of immune mediated ocular disease. We investigated the expression of ICAM-1 on the ocular surface of the rat eye following subconjunctival administration of IFN-gamma. A dose response study was performed using 100, 1,000 and 10,000 IU IFN-gamma/dose. The presence of ICAM-1 was determined using a standard immuno-peroxidase staining technique. The cornea, limbus, and conjunctiva were evaluated. The degree of reaction product in each area was graded by a masked observer. We found constitutive expression of ICAM-1 on the conjunctiva but not on the cornea. There was a significant relationship between the dose of IFN-gamma and the intensity of ICAM-1 staining on the conjunctiva (p < or = 0.05) and on the limbus (p < or = 0.04). Subconjunctival IFN-gamma had no effect on the expression of ICAM-1 in the cornea.