Systemic B-cell depletion and clinical remission of the systemic effects of cryoglobulins have been achieved in hepatitis C virus-positive immunocompetent patients with rituximab, a human/mouse chimeric monoclonal antibody that specifically reacts with the CD20 antigen. Thus, this provides a rationale for the use of rituximab for type III cryoglobulin-related graft dysfunction in renal-transplant patients. Seven patients, of whom five were hepatitis C positive, developed renal function impairment long after transplantation, as well as de novo nephrotic syndrome (n = 5), severe hypertension (n = 5), nephritic syndrome (n = 1), and increased serum creatinine (n = 1). This type III cryoglobulinemia was associated with membranoproliferative glomerulonephritis and with thrombi within the glomeruli in one case. In addition to their baseline standard immunosuppressive medications, the patients were given weekly rituximab infusions: 375 mg/m(2) for 2 weeks in four cases, for 3 weeks in one case, and for 4 weeks in two cases. This treatment resulted in a dramatic improvement in all renal parameters, particularly a sustained remission of nephrotic syndrome in three cases, the disappearance of nephritic syndrome in one patient, and improved nephrotic syndrome in two cases, as well as a sustained clearance of cryoglobulins in six cases. However, it also resulted in severe infectious complications in two cases. We concluded that rituximab therapy is effective in cryoglobulin-related renal dysfunction in renal transplant patients but, due to chronic immunosuppression, this may be achieved at the expense of infectious complications.