Recently, a high incidence of novel N-glycosylation sites introduced by somatic mutation was observed in the immunoglobulin variable region genes of follicular lymphoma. As these are positively selected and are uncommon in normal B cells, they may have a role in tumour growth and behaviour. Sites are not characteristic of chronic lymphocytic leukaemia or myeloma, but are detectable in approximately 50% of diffuse large cell lymphomas. Another feature of the variable region genes of certain lymphomas is ongoing somatic mutation. To determine whether glycosylation is associated with this phenomenon, we analysed variable region gene sequences of Burkitt's lymphoma (BL) and mucosa-associated lymphoid tissue (MALT) lymphoma. Novel sites were common in endemic BL (82%) and in 4/5 patients with Iranian BL. However, sporadic BL had a lower incidence (43%). Patients with MALT lymphoma had a low frequency (9%) of novel sites, comparable to normal B cells. These findings distinguish glycosylation sites from ongoing mutation and may reflect different environmental influences on these tumours.