Methods Patients. Fourteen children, nine boys and five girls, 2 to 14 years of age, with MCNS were studied. All patients had a clinical history of edema, heavy proteinuria (greater than 40 mg/rn2 body surface arealhr) and hypoalburninemia (less than 25 glliter). Renal biopsy specimens showed no, or minimal, mesan-gial changes by light microscopy and no, or scanty, deposits of IgG and/or 1gM by immunofluorescence microscopy. In 12 patients the renal biopsy specimens were performed close in time to renal function tests; the mean time interval was 2.9 [1—6] days. In the remaining two patients the time interval between the two investigations was longer. All children and their parents gave their informed consent to the investigations. The study was approved by the Ethical Committee of the Karolinska Institute, Huddinge, Sweden.

Renal function tests. Renal function was evaluated by GFR and ERPF measured as clearances of inulin and PAH, respectively. A standard clearance technique was used, including a continuous infusion of inulin (Inutest, 25%, Laevosan-Gesell-schaft, Linz, Austria), 1.4 mg/kg of body weight/mm, and PAH (arninohippurate sodium, 20%, MSD), 0.2 mg/kg of body weight/mm, after a prime dose of inulin 60 mg/kg of body weight, and PAH 9 mg/kg of body weight. After an equilibration time of 1 hr, four to six urine collection periods followed. A blood sample was drawn midway during each collection period.