It is altogether appropriate that the gut should possess efficient immunological defences given the interface between its antigen-rich contents and the permeable mucosa. More than that, however, the gut is an important immunological organ in its own right. In this respect, the gut mucosa contains more lymphocytes than all other organs of the immune system combined. It is estimated that in humans a metre of intestine contains 10¹⁰ lymphocytes, which is almost equivalent to the number contained in the spleen.1 In the light of this quantitative difference and the fact that intestinal lymphoid tissues are subject to constant immunostimulation, it might be expected that a larger proportion of lymphomas would arise from the intestine than the peripheral lymphoid system but, curiously, the contrary is true. Although the gastrointestinal tract is the commonest site of extra-nodal lymphoma in Western countries, only 10% of lymphomas overall arise there.2 There are, however, significant differences in the types of lymphoma that arise in the gut compared with the peripheral lymphoid tissues. Thus, both Hodgkin’s disease …