A single use, sterile, self-contained, compact, easy to use centrifugal separation unit provides for quick, reliable platelet concentration from whole blood. Anti-coagulated blood is injected through an elastomeric seal into a separation chamber featuring a tapered barrel and an end cap. At least one port is located in the end cap, at a desired radius from the longitudinal axis. The centrifugal field created by rotation of the chamber stratifies the blood radially, with red blood cells adjacent the wall of the barrel, and plasma found closest to the longitudinal axis. Opening the port causes the pressure of the centrifugal field to eject red blood cells or plasma, thereby increasing the concentration of platelets remaining in the chamber. After ceasing chamber rotation, the concentrated platelets are recovered.