Inappropriate erythropoietin production is the main defect responsible for the anemia of chronic renal failure. However, many other factors can contribute. There is support for the existence in uremic serum of substances that can inhibit erythropoiesis and cause hemolysis, but it is still debated how far uremic retention solutes contribute to the pathogenesis of anemia during chronic renal failure. This article looks at the role of uremic toxicity in exacerbating the anemia of chronic renal failure.