--Disease Characteristics-- Histologically confirmed immunoglobulin A nephropathy (IgAN) Patients must have either: - Persistent severe proteinuria alone (urine Pr/Cr ratio at least 1.0) OR - Moderate proteinuria plus renal biopsy changes indicating risk of progression (glomerulosclerosis or proliferation) --Prior/Concurrent Therapy-- Endocrine therapy: At least 1 month since any prior prednisone No more than 3 months of prior prednisone therapy since renal biopsy Other: At least 1 month since any prior immunosuppressive therapy or fish oils No more than 3 months of prior immunosuppressive therapy or fish oil administration since renal biopsy --Patient Characteristics-- Hepatic: Bilirubin less than 2 times upper limit of normal (ULN) AST less than 2 times ULN No known chronic liver disease Renal: Protein excretion greater than 0.5 g/1.73 m2/24 hours OR Urine protein/creatinine ratio greater than 0.5 on 2 occasions at least 4 weeks apart in the 6 months prior to study Creatinine clearance at least 50 mL/min Other: No systemic lupus erythematosus No Henoch-Schonlein purpura No diabetes mellitus, cataracts, aseptic necrosis of any bone, or other conditions potentially exacerbated by prednisone therapy Not pregnant Adequate contraception required of all fertile patients