Abstract A benzidine-nitroprusside stain for erythrocytes in the urinary sediment is described which we believe to be specific for red blood cells and fragments thereof. With this technique the red blood cells stain a deep blue-purple and are easily distinguished from contaminants and other formed elements of urine. The stain is based upon the pseudoperoxidase reaction of hemoglobin and benzidine. The nitroprusside may act as a catalyst. The granules of fine and coarse granular casts take on the same bluish-purple stain. This finding suggests fragments of red blood cells as the origin of the granules and helps explain the more serious implication of granular casts. Erythrocytes may occur in the urinary sediment of normal individuals up to approximately 2 per high-power field. This level, determined by a conversion of the results of quantitative studies to the methods employed in analyzing single specimens, is supported by the results of our findings in 3,000 consecutive urinalyses in young men applying for employment. In this series, only 1.2 per cent of specimens contained more than 2 red blood cells per high-power field. The preservative tablet and formaldehyde are efficient agents for the preservation of erythrocytes. Thymol, toluene, chloroform, and boric acid are not satisfactory. None of these substances interfere with the stain for erythrocytes.