Cryoglobulins were studied in the sera of 40 unselected pSS patients. The nature of the cryoglobulins was defined using a very fast and sensitive resolution electrophoresis technique combined with immunofixation. Thirty-five per cent of SS patients were shown to have circulating IgMk mixed monoclonal cryoglobulins. On the contrary, all the other tested cryoprecipitates were found to be mixed polyclonal, with the exception of one patient with SLE. The presence of cryoglobulins in the sera of SS patients correlated with extraglandular disease and with autoantibodies to Ro (SSA) cellular antigen and rheumatoid factor. Patients with cryoglobulins had lower serum C4 levels compared to patients without cryoglobulins. These findings suggest that SS in addition to polyclonal B-cell hyperreactivity expresses a monoclonal process preceding the development of lymphoid neoplasia. Extraglandular manifestations of the syndrome may be associated with an immune complex mediated pathology.