Abstract: A centrifuge rotor and apparatus for the determination of whole blood micro-hemotocrits for in vitro diagnostic use. The centrifuge rotor comprises a base with at least two inner tube retainers and at least two outer tube retainers. An elongated hole is provided in both of the tube retainers for securely positioning a tube containing blood onto the centrifuge rotor. As the centrifuge rotor is subjected ot rotary action, the tubes are held in place by centrifugal force in conjunction with the inner and outer tube retainers and neither central lateral support for the tubes nor a separate cover is required for use of the rotor or apparatus.