renal vasculitis of small and medium-size vessels are Introduction frequent. In less severe cases, a mesangial lesion may be seen [2]. Mixed cryoglobulinaemia (MC) is a rare systemic disease characterized by circulating cold precipitable mixed immunoglobulins composed of monoclonal IgM rheumTreatment of MC nephritis atoid factor and polyclonal IgG. Purpura, weakness, arthralgias and glomerulonephritis are the principal clinical manifestations. Rarely gastrointestinal, cardiopGood blood-pressure control is of paramount importance in patients with MC nephritis. Arterial hypertenulmonary and neurological vasculitis may also occur. Liver disease is frequent. Some patients may remain sion is common and often severe in MC patients. As in any type of renal disease, hypertension contributes asymptomatic for years but in many cases the liver disease is progressive and this is a frequent cause of to progression and to cardiovascular disease. The latter represents the main cause of death among patients death. MC was called essential until recently because no aetiological factor could be identified. In 1990, with MC [3]. Therefore, every effort should be made to maintain blood pressure within the range of recomhowever, Pascual et al. [1] reported an association between MC and hepatitis C virus (HCV ) infection. mended values. A combination of antihypertensive agents is usually necessary to achieve this goal. Since then it has been recognized that the majority of patients with MC had anti-HCV antibodies and a Because of the frequent association of MC with HCV infection, treatment with the antiviral agent critical aetiological role has been attributed to HCV infection. a-interferon (aIFN ) is one therapeutic option which has been recommended in MC patients. In two randomized trials [4,5], doses ranging between 1.5×106 Cryoglobulinaemic nephritis and 3×106 Units were administered three times a week for 23–52 weeks. HCV RNA turned negative in about half of the 42 patients (53%). Most patients had only Kidney involvement is frequent in MC, but in many mild renal involvement and only a few had modercases renal disease is recognized only years or decades ate renal insufficiency. Improvement of systemic signs after HCV infection. In a few patients, however, renal and serological markers of disease activity such as and extrarenal signs and symptoms are present at the S-creatinine or circulating cryoglobulins, usually onset of the disease. The clinical presentation of renal occurred within the first month. Unfortunately, all the disease may be variable. A number of patients show patients who responded had a relapse of the disease proteinuria, microscopic haematuria and/or arterial upon discontinuation of aIFN. More recently a few hypertension. Moderate renal insufficiency is frequent. case reports have shown longer remission when higher In another 20% of cases renal involvement is heralded doses of aIFN, up to 10×106 Units three times a by a nephrotic syndrome. In some 20–30% of patients week, were given for a short period [6–9]. Anecdotal the first renal manifestation is an acute nephritic synobservations of reversal of membranoproliferative drome with microscopic or macroscopic haematuria, glomerulonephritis after aIFN have also been reported proteinuria and a rapidly progressive deterioration in [10]. From the available information it seems, however, renal function. A diffuse proliferative and exudathat the benefit of aIFN is transient and is confined to tive glomerulonephritis resembling a membranoprofew patients with mild and/or quiescent renal disease. liferative glomerulonephritis is the most common It remains unproven whether aIFN plays a favourhistological pattern observed. Intraluminal thrombi, able role at all in patients with flares of renal activity glomerular infiltration of monocytes, double-contour or with renal insufficiency. From a theoretical point of appearance of the glomerular basement membrane and view, aIFN may even be contraindicated in patients with active renal disease, as its immunostimulating Correspondence and offprint requests to: Mariarosaria Campise MD, activity might aggravate renal disease and vasculitic Divisione di Nefrologia e Dialisi, Ospedale Maggiore, IRCCS Via Commenda, 15, I-20122 Milan, Italy. lesions [11]. Furthermore, aIFN has myelosuppressive