SUMMARYThe V«IV gene encoding the light chain of an IgA RF has been shown to have undergone 31 somatic mutations compared with the single existing VKIV germ-line gene. We now show the persistence of the rearranged and mutated DNA coding for this RF over a period of 5 years in the peripheral blood lymphocytes (PBL) of the patient with rheumatoid arthritis (RA), The sequence of the RF has been conserved to identity over this period. These results raise the possibility that the particular antigenic stimulus leading to RF production in this RA patient is active over a long period of time.