In chronic renal disease, the severity of proteinuria is associated with the rate of renal function loss. Proteinuria, therefore, was postulated to play a role in the final common pathway of chronic renal function loss. If so, reduction of proteinuria would improve long-term renal outcome. Improvement of long-term renal function outcome has been obtained in several intervention trials; in these studies; regimens providing better renoprotection were associated with more effective reduction of poteinuria than control regimens. As the reduction of proteinuria is mostly associated with a fall in blood pressure, however, it is difficult to delineate the respective roles of the lowering of blood pressure and of proteinuria. Interestingly, the initial reduction of proteinuria (but not of blood pressure) by antihypertensive treatment appears to predict long-term renal outcome in man as well as in experimental renal disease. This suggests that an intervention strategy aimed not only at the normalization of blood pressure, but also specifically at elimination of proteinuria, might be able to improve long-term renal outcome in proteinuric patients. If so, this would provide further evidence in support of the hypothesis that proteinuria is causally involved in the progression of long-term renal function loss.