BN, but not LEW, rats treated with subcutaneous injections of mercuric chloride (HgCl2) develop an autoimmune syndrome with infiltration of mononuclear cells into various organs including the oral mucosa. In the present study, we have utilized autometallographic techniques to visualize mercury in the oral mucosa, salivary and lacrimal glands of mercury-sensitive BN and -non-sensitive LEW rats injected with HgCl2. Mercury was deposited intracellularly in dendritic cells that were scattered throughout the lamina propria and submucosal connective tissue of both rat strains. In addition, mercury was detected in dendritic cells appearing within small cell clusters in the juxtaepithelial connective tissue of BN oral mucosa. In salivary and lacrimal glands, mercury was found in dendritic cells scattered throughout the stroma as well as in mononuclear cell foci. Mercury was also found in ductal epithelium. No staining was seen in any of the non-mercury-treated controls. Phenotypic analysis revealed that most mercury-laden cells were ED2+ resident macrophages and that some, but not all, of these cells expressed MHC class II antigens (RT1B).