The theory of 'homing' mechanism has been proposed to explain the association of malignant lymphoma involving multiple sites of mucosa-associated lymphoid tissue (MALT). DNA rearrangement in the peripheral blood and bone marrow specimens of 20 patients with MALT lymphoma were studied utilizing JH and C beta gene probes, aiming to detect circulating lymphoma cells and unrecognized bone marrow involvement. Our search for malignant cells in the peripheral blood was unrewarding and the 'homing' theory remained unproven. However, the study of DNA rearrangement showed to be useful in determining the malignant nature of abnormal lymphoid aggregates found in the bone marrow of these patients.