The association of anemia with uremia is a striking one. However, just as the actual pathogenesis of the signs and symptoms associated with renal disease is poorly understood, so also is the mechanism of development of anemia in this syndrome. It is the purpose of these investigations to evaluate the relative importance of productive and destructive defects and to correlate them with the clinical state. Methods and Materials Hemoglobin was measured according to Crosby et al.1 Reticulocytes were counted by the dry method and expressed as per cent of the 1000 cells counted. Osmotic fragility was measured according to the technique of Shen2 and increment curves plotted and compared as previously described. Mechanical fragility was measured by a modification of the method of Shen et al.,4 with use of rotation of 35 rpm and a radius of 13 cm. Time intervals varied from 90 to 270 minutes.