3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid, which cannot be removed by conventional hemodialysis due to its strong albumin binding, was found to be efficiently removed by continuous ambulatory peritoneal dialysis (CAPD), resulting in a lower serum level in uremic patients on CAPD than in those on hemodialysis. 3-Carboxy-4-methyl-5-propyl-2-furanpropionic acid was demonstrated in vitro to inhibit erythroid colony formation. The anemia in patients on CAPD was significantly less severe than in those on hemodialysis. These results suggest that the efficient removal by CAPD of 3-carboxy-4-methyl-5-propyl-2-furanpropionic acid, an inhibitor of erythropoiesis, is related to an improvement of anemia in patients on CAPD.