The majority of low grade gastric lymphomas arise within acquired organized lymphoid tissue, which has all the features of MALT. This MALT is specifically acquired most commonly in response to infection of the gastric mucosa by H pylori. The lymphocytes within this MALT are therefore programmed to respond to this organism and the neoplastic cells of the lymphoma that may develop within this acquired MALT retain the ability to respond to the immunological proliferative drive associated with the continued presence of the organism. Following the removal of this immunological drive by eradication of the organism in vivo, the lymphoma shows clinical and histological regression. The time required to see this response is unknown and there are some lymphomas that fail to respond to simple Helicobacter eradication. In some cases, there is continued molecular evidence of the presence of the lymphoma clone in low levels and the significance of this remains unknown. These factors are presently under detailed examination, and several clinical trials to assess the response of a large series of low grade gastric MALT lymphomas to anti-Helicobacter therapy and the requirement for additional chemotherapy are at present in progress.