Abstract: A decanting centrifuge for processing liquid material in cylindrical open-topped sample tubes supported on the rotor and movable from a first position with the open ends directed towards the rotor axis and a second position for decanting supernatant from the sample tubes under the influence of the centrifugal force. In the second position the sample tubes are horizontal or include a relatively small angle with the horizontal, and the radially outermost generatrix of the inner surface of the sample tubes is tangent to an imaginary circular cylindrical surface concentric with the rotor, the tangent point being spaced by a predetermined distance from the closed bottom end of the sample tubes, so that a predetermined volume is retained between the tangent point and the bottom end.