Nephrotic range proteinuria, defined as 24 hour urine protein excretion greater than or equal to 3.5 g/d in adults and children weighing greater than or equal to 70 kg and greater than or equal to 50 mg/kg in adults or children weighing less than 70 kg. Proteinuria will be assessed with at least three 24 hour urine collections obtained during the baseline period (for these collections, there is no minimum period, the maximum period is 3 months prior to study entry, and the most recent must be within 1 month of entry). These measurements will be obtained while on angiotensin antagonist therapy (if tolerant of this medication) and will exclude urine collections judged inadequate based on creatinine appearance. For patients in the drug overlap group, baseline proteinuria will be determined from patient's records demonstrating on at least one urine collection, proteinuria greater than 3.5 g/d while off immunosuppressive therapy.