Conjunctival biopsy specimens from 8 OCP (ocular cicatricial pemphaigoid), 6 AKC (Atopic keratoconjunctivitis) patients, and 10 normal individuals were studied for the expression of HLA class II molecules. Immunohistochemical studies were performed using monoclonal antibodies specific for HLA DR, DP, and DQ molecules. Strong, diffuse staining in conjunctival epithelium was observed for HLA DR in the specimens of OCP and AKC patients with heavy staining in the superficial and basal epithelial layers, not observed with normal specimen. About 30% of the samples from OCP and AKC patients showed a similar pattern of the diffuse staining in the superficial epithelial cell layers for HLA DP with less intensity than for HLA DR, while the 50% of the samples had shown greater HLA DP positivity in the basal epithelial cell layers. Positive epithelial cells and positive inflammatory cells were also observed in these samples while normal epithelium had few HLA DP positive cells. The HLA DQ staining pattern was similar to that observed for the HLA DP. There were significant increases over normals in the numbers of HLA-DR positive cells within the substantia propria of OCP and AKC specimens with the majority of the positive cells located subepithelially and around vessels. Increased numbers of HLA DP and HLA DQ positive cells were seen in the substantia propria of CP and AKC specimens with the staining pattern similar to the HLA DR while normal specimens had little staining in this region. Vessel endothelial cell staining was observed for HLA DR, DP and DQ with different degrees of the staining in these three groups.(ABSTRACT TRUNCATED AT 250 WORDS)