Sixteen children with biopsy-confirmed type I membranoproliferative glomerulonephritis (MPGN) were treated with six alternate-day intravenous pulses of methylprednisolone followed by single-dose alternate-day prednisone for 12-66 months (mean 37 months). The average length of follow-up was 52 months (range 12-127 months). Compared with pretreatment values, the frequency of hematuria (13/16 vs. 8/16, P < 0.05) and the levels of serum albumin (2.66 +/- 0.69 vs. 3.76 +/- 0.39 g/dl, P < 0.001), creatinine clearance (97 +/- 37 vs. 129 +/- 26 ml/min/1.73 m2, P < 0.001), and proteinuria (5.2 +/- 5.1 vs. 1.0 +/- 0.8 g/day, P < 0.001) were significantly improved after 3 months of therapy. Improvement has persisted through the end of the follow-up period. Repeat kidney biopsies showed a significant reduction in acute changes but an increase in chronic changes. Thirteen patients have been off therapy from 1 to 74 months (mean 20.8 months). Nine have a normal urinalysis, creatinine clearance, and protein excretion. The remainder have normal renal function but proteinuria ranging from 3.2 to 4.3 g/day. The data support the evidence of other investigators that corticosteroid therapy is beneficial in type I MPGN and suggest that initiation with pulse methylprednisolone may promote early stabilization of the disease.