Paraffin sections of surgical and autopsy material from 12 cases of primary non-Hodgkin's lymphomas of the central nervous system were examined for histopathological diagnosis and for the demonstration of cytoplasmic immunoglobulins. According to the Kiel classification, there were five cases of lymphoplasmacytoid polymorphous lymphoma, five of immunoblastic lymphoma, one of lymphoblastic lymphoma of convoluted cell type. There was also one of the recently described multilobated lymphoma. An immunohistological study of light and heavy chains by peroxidase-antiperoxidase (PAP) technique and avidin-biotin complex (ABQ)technique was performed. Intracellular immunoglobulins were demonstrated in seven cases: four cases were classified as immunoblastic lymphomas and three cases as lymphoplasmacytoid lymphomas. Negative immunoglobulin staining was observed in five cases: two lymphoplasmacytoid lymphomas, one immunoblastic, one lymphoblastic of convoluted cell type and one multilobated. A ‘monoclonal’ pattern of immunoglobulin staining was detected in six cases. One case, classified as immunoblastic lymphoma, showed ‘bitypic’ staining for k and λ chains. It was concluded that primary CNS non-Hodgkin's lymphomas of the present series showed morphological and immunohistological features similar to those of malignant lymphomas arising in extraneural sites. In particular, the presence in our series of a multilobated lymphoma, as a primary CNS tumour, is emphasized.