Abstract: A fluid layering device for use with a syringe to facilitate layering a liquid from the syringe onto a denser liquid contained in an open-top centrifuge tube. A fitting in the device is releasably attachable to the syringe for receiving liquid therefrom. An elongate nozzle carried on the fitting has a pair of opposed end faces, and a pair of flow-constricting bores communicating associated nozzle end faces with liquid received in the fitting. An annular step formed on the fitting is engageable by friction fit with the tube's upper open end to hold the nozzle at an axially aligned position within the tube. At this position, each of the nozzle end faces confronts, and is spaced from, an inner wall portion in the tube by a clearance which is adapted to produce, with liquid being forced from the syringe through the associated bore in the nozzle, a controlled-flow ribbon of liquid down the wall of the tube onto the upper surface of the denser liquid in the tube.