To investigate the mechanisms responsible for lymphocyte accumulation in the eye in uveitis, we examined iris biopsy specimens that were obtained from 10 patients with uveitis and from 12 patients with cataract for the presence of adhesion molecules on vascular endothelium, uveal cells, and infiltrating inflammatory cells. Immunoperoxidase staining of iris biopsy specimens that were obtained from patients with uveitis revealed an increased expression of intercellular adhesion molecule 1 (CD54) on endothelial cells, lymphocytes, fibroblasts, and iris epithelial cells. Seven of the 10 iris biopsy specimens that were obtained from patients with uveitis had a significant inflammatory cell infiltrate. Lymphocytes (CD2 positive) that infiltrated the iris were predominantly helper T cells (70%) and strongly expressed the lymphocyte function-associated antigen 1 (CD11a, CD18) molecule, the ligand for intercellular adhesion molecule 1, in four of the seven biopsy specimens. In contrast, small numbers of lymphocytes were evident in only three (25%) of the iris biopsy specimens that were obtained from patients with cataract. Vascular endothelium from the latter group did not express intercellular adhesion molecule 1 or endothelial leukocyte adhesion molecule 1. The results of this study revealed the enhanced expression of vascular endothelial cell and lymphocyte adhesion molecules in the iris biopsy specimens that were obtained from patients with uveitis. The presence of these receptors and their presumed ligands may have important implications for the role of these molecules in the pathogenesis of uveitis.