Dietary protein restriction in the treatment of symptomatic renal failure has been utilized for many years, especially as a means for reduction of 'fixed acid" load. Studies in animal models of renal failure suggest that low protein intake may retard the progression of renal disease as well. However, large, well-organized investigations into this question in humans have fallen prey to difficulties that are almost impossible to overcome. Chief among these difficulties is the problem of chronically reducing protein intake in patients with a lifelong intake far above the recommended daily allowance (RDA). Another is the fact that all previous studies have been performed in patients with moderate to severe compromise of renal function. Thus, the potential efficacy of reduced protein intake in the retardation of the progression of renal disease remains an open question. In this article, we discuss the current state of knowledge and propose an approach to answering this question.