Experimental autoimmune dacryoadenitis was induced in 100% of Lewis rats by immunization with a KCl extract of Harderian gland in complete Freund's adjuvant (CFA), providing that the animals had received simultaneously i.v. injection of killed Bordetella pertussis. No significant pathological changes in the Harderian gland were observed in control animals immunized with KCl extracts of lacrimal or salivary glands. Gel filtration of the KCl extract on Sephacryl S-300 column yielded three protein fractions. Fraction II (MW = 50-100K) induced severe Harderian gland disease following a single injection of 2.0 mg protein in CFA plus pertussis. The initial lesions consisted of multiple focal infiltrates of mononuclear cells. Later, the inflammatory process assumed a more granulomatous form, with significant contribution by epithelioid and giant cells. In contrast, Lewis rats immunized with Harderian gland fractions I or III proteins, or with extracts of lacrimal or salivary gland, showed little or no inflammatory lesions. These data suggest that Harderian gland contains unique tissue-specific autoantigen(s) capable of inducing autoimmune granulomatous dacryoadenitis in the rat.