We report 10 cases of monocytoid B-cell lymphoma, five of which had extranodal lymphomas of mucosa-associated lymphoid tissue (MALT) type. In one patient the MALT lymphoma in the salivary gland was microscopic. In another, the small bowel lymphoma, which preceded the monocytoid B-cell lymphoma by 11 years, showed different clonal immunoglobulin gene rearrangements. Attention is drawn to the extreme degree of plasmacytic differentiation and epithelioid cell infiltration that may occur in monocytoid B-cell lymphoma. In addition to the cytological and immunophenotypic likeness of monocytoid B-cells and centrocyte-like cells, monocytoid B-cell and MALT lymphomas share a number of micro-anatomical and behavioural characteristics. These include the sharp separation of the monocytoid B-cells and plasma cells, follicular colonization and progression to high-grade lymphoma. It is suggested that the frequent association of monocytoid B-cell lymphoma with Sjögren's syndrome may be due to the fact that the salivary glands drain to cervical lymph nodes that are part of the systemic, rather than the mucosal, lymphocyte circulation pathway.