Lymphomas of the gastrointestinal tract are divided into those with low grade and those with high grade malignancy. With this classification corresponds also the morphology of the tumour cells. In the former case the tumour cells are small to intermediate centrocytic-like cells (so-called CCL cells; intermediate cells). The association of this type of ML to Helicobacter pylori is known. In experiments similar changes occurred in ferrets after infection with Helicobacter mustelae and in BALB/c mice with Helicobacter felis. It is important to differentiate lymphomas with a low malignity from mantle cell lymphomas. The lymphoma has a similar morphology but more aggres- sive behaviour than MALT lymphomas from CCL cells. The latter are derived from the cells of the marginal zone of follicles. The immunophenotype of low grade malignant MALT lymphomas is: CD 20+, IgM+, CD 5-, CD 10-, CD 23-, cycline D1-. As to cytogenetic properties, trisomy 3 and t (11;18) is usually present. In some instances on cryostat sections a so-called aberrant immunophenotype may be found. In highly malignant lymphomas centroblast-like cells are present or they are in a mixed population together with centrocytes. In ML of this type with high staging it is difficult to differentiate secondary lymphomas. As a rule ML stage IV are not included among primary lym- phomas of the stomach or colon. In this respect the use of antibodies against Bcl-2 oncoprotein is problematic. The positivity of the Bcl-2 oncoprotein is not only the result of chromosomal translo- cation as known in malignant lymphomas of the germ centre of lymphatic follicles.

        Key words: malignant lymphomas – gastrointestinal tract