Experimental autoimmune uveoretinitis (EAU), induced in (LEW X BN) F1 rats by immunization with S antigen (S-Ag) is T cell and antibody (ab) mediated and anti-S-Ag IgE ab have been involved in the occurrence of ocular lesions. (LEW X BN) F1 rats repeatedly injected with HgCl2develop an autoimmune disease characterized by numerous auto-ab and a high increase of serum IgE level. We hypothesize that large amounts of non anti-S-Ag IgE induced by HgCl2would compete with anti-S-Ag induced by S-Ag immunization so as to prevent EAU to occur. Indeed (LEW X BN) F1 rats immunized with S-Ag 7 days after the first HgCl2injection are strongly protected against EAU. The putative role of the different mercury-induced autoimmune phenomena in the protection against EAU are discussed.