The aim of our study was to determine whether immunosuppressive treatment is effective in preventing and reversing the evolution of Berger's disease toward chronic renal failure. We studied 20 unselected, consecutive patients with biopsy-proven Berger's disease who met the criteria for disease progression. They had proteinuria, significant histologic changes, persistent hematuria, and red cell casts. The treatment consisted of prednisone in an alternate-day regimen and cyclophosphamide, either in a daily oral administration or in a monthly intravenous pulse injection, both given for a 6-month cycle. Five patients had chronic renal failure (as disclosed by plasma creatinine of 230 +/- 71 mumol/L), hypertension, and proteinuria (2.7 +/- 0.8 gm/day), whereas the remaining 15 patients had normal renal function (plasma creatinine, 97 +/- 18 mumol/L) and less severe proteinuria (1.9 +/- 1.1 gm/day). However, even these 15 patients had a significant number of risk factors heralding progression to chronic renal failure. Over an average follow-up of 8.7 +/- 3.7 years (range, 5 to 15 years), all patients but one had complete disease remission, including five patients with incipient chronic renal failure. Relapse occurred in two patients who were healed after a repeat treatment cycle. Over the entire follow-up period, no patient progressed to chronic renal failure and plasma creatinine concentration remained stable, even in subjects in whom it was high before treatment (257 +/- 79 versus 230 +/- 71 mumol/L; p > 0.05). The immunosuppressive treatment of patients with Berger's disease with high probability of progression appears to be effective in the prevention of end-stage renal disease.