A patient is described with Sjögren's syndrome and an IgM-kappa gammopathy. With time cryoglobulins, the cause of acute renal failure, could be detected. The kidney biopsy showed a proliferative glomerulonephritis as is frequently seen with mixed cryoglobulinaemia. Plasmapheresis and immunosuppression resulted in long-term improvement of kidney function. The differential diagnosis of acute renal failure of glomerular origin in a patient with Sjögren's syndrome is discussed. This case report illustrates once more the consequences of monoclonal B-cell lymphocyte activation in Sjögren's syndrome.