Abstract: Centrifugal batch separation of blood in a closed collapsible container is carried out by placing the container in a rigid casing in which the container is divided into two or more sections in that the casing constricts the container at one or more predetermined positions between the ends of the container. The casing with the container therein is then centrifuged, a gap-like passage between the container sections permitting rearrangement of the contents of the container so that each section will accommodate a blood fraction. After the centrifugation the fractions are isolated from each other. The volume of the cavity within the casing accommodating the radially outermost container section is matched with the hematocrit and the total blood volume by means of filler bodies.