A 38-year old patient had been suffering, since the age of 17, from membranoproliferative glomerulonephritis associated with chronic atopic eczema and recurrent sinusitis. Bouts of eczema with severe itching occurred simultaneously with sinusitis and proteinuria. Permanently extreme serum IgE levels (greater than 10,000 IU/ml), defective neutrophil chemotaxis and monocyte phagocytic function (Buckley's syndrome) were present. Because cyclosporin reduces excessive IgE levels in Brown Norway rats with mercuric chloride nephritis, we gave the patient this drug in daily doses of 3-4 mg/kg. A dramatic improvement resulted within a few days: itching disappeared, the eczema progressively cleared, proteinuria decreased to less than 0.5 g/day and serum IgE levels to 4000 KIU/l. Reduction of dosage was followed by recurrence of all clinical and biological signs. In spite of the improvement obtained, serum creatinine levels, which were initially high (200-250 mumol/l) rose up to 300 mumol/l after one year of treatment.