Abstract: A centrifugating device for biological liquids, e.g. blood, in which a rotatable container carries a specially shaped seal that surrounds and bears on a fixed assembly with a minimum area of interface between the fixed and rotating parts. This seal is disposed outside the path of the liquid to be treated. The fixed assembly, in turn, is releasably carried by a bracket, the bracket being selectively longitudinally extensible as well as selectively adjustably swingable about a vertical axis of oscillation eccentric to the centrifuge, thereby to permit exact positioning of the fixed assembly coaxially of the rotatable container. The parts are so simple and inexpensive in construction that at least some of them can be used once and thrown away. Moreover, the fixed assembly is easily insertable in sealed relationship in any of a variety of containers, by the simplest of manual assembly and disassembly operations.