Lymphocyte subsets in the salivary gland and kidney were examined in a 38 years-old female patient with Sjögren's syndrome associated with interstitial nephritis by PAP immunoperoxidase method using monoclonal antibodies. Predominant cells of the infiltrating cells in both tissues were T lymphocytes and most of them were Ia+, OKT4+ cells (activated helper/inducer T lymphocytes). A small number of T lymphocytes were OKT8+ (suppressor/cytotoxic T lymphocytes). Moreover, we found the OKT8+ cells invading the salivary duct epithelial cells. There was no difference in the proportion of lymphocyte subsets of the infiltrating cells between the salivary gland and kidney. A similar pathologic mechanism of tissue damage, therefore, was suggested in both tissues.