Abstract: An apparatus for the separation of blood components, specifically for the removal of white blood cells and blood platelets from blood comprises a tubular housing providing at one end thereof with a blood inlet and at the other end thereof with a blood outlet and an aggregate layer of fibers capable of sequestering white blood cells and blood platelets packed in the housing. The aggregate layer of fibers comprises a blood inlet side layer of a bulk density of not less than 0.16 g/cm.sup.3 and less than 0.21 g/cm.sup.3 and a blood outlet side layer of a bulk density of not less than 0.21 g/cm.sup.3 and not more than 0.23 g/cm.sup.3 and is packed in a ratio in the range of 0.04 to 0.09 g per ml of the flow volume of blood under treatment.