Forty-five cases of myoepithelial sialadenitis (MESA) were investigated histologically, immunologically, and clinically. Two patients with clinical evidence of Sjögren's syndrome were also included in the study, though salivary gland biopsies showing MESA were not available. A total of 16 patients had Sjögren's syndrome or another type of autoimmune disease. In 42 cases of MESA, so-called proliferation areas composed of immunoblasts and lymphoplasmacytoid cells were found. The proliferation areas were small and circumscribed in 16 cases, and extensive and confluent in 26 cases. All the confluent proliferation areas analyzed with the immunoperoxidase (PAP) method showed a monotypic immunoglobulin pattern (predominantly IgM/). Extrasalivary malignant lymphoma with the same histologic and immunohistologic features as the confluent proliferation areas was found in 14 patients. Thus, this type of MESA is called manifest malignant lymphoma. The tumor was classified as LP immunocytoma in 23 patients, and as LP immunocytoma transforming into immunoblastic lymphoma in three patients. One patient developed nodal B-immunoblastic lymphoma. The term early lymphoma is suggested for MESA with circumscribed proliferation areas showing a monotypic immunoglobulin pattern (usually IgM/), because extrasalivary malignant lymphoma developed later in four of the patients with this type of MESA. The two patients with only clinical evidence of Sjögren's syndrome also showed extrasalivary malignant lymphoma (LP immunocytoma in one case and immunoblastic lymphoma in the other).