In 20 patients under regular dialysis with an arteriovenous fistula in one forearm, platelet counts were measured in blood taken simultaneously from the cubital vein, the arterialized vein near the site of anastomosis, the femoral vein, and the femoral artery. Samples of blood from the fistula and from the cubital vein of the opposite limb were taken with and without stasis. The highest values were found in blood taken from the cubital vein without stasis. Platelet counts were identical in femoral artery and vein, but were 4.8 and 4.9%, respectively, lower than the cubital vein values. Platelet counts from fistula blood taken without stasis were 13.7% lower than in the cubital vein. Platelet counts were lower when samples of blood were taken with stasis: 11.2% in the cubital vein, 7.4% in fistula blood. The awareness of these differences is of practical importance for platelet behavior studies.