Clinical and laboratory investigations were performed on a patient presenting with xerostomia and swelling of the parotid gland. Lymphoid infiltration of the salivary glands (parotid and labial) and paraproteinaemia were found. Immunoperoxidase studies of labial and parotid glands revealed that local immunoglobulin synthesis was essentially polyclonal although monoclonal staining of Russell bodies within the labial tissue suggested that at least some of the serum paraprotein was being synthesised locally. The implications of these findings are discussed in terms of diagnosis and treatment.