All existing centrifuges have a resolving power that is proportional to their centrifugal field, G = omega(2)R, raised to the first power. By combining conventional sedimentation with field-flow fractionation in a two-dimensional separation system, it is possible to devise a continuous rotor whose selectivity is proportional to the second power of its centrifugal field. This extraordinary result suggests that a hybrid rotor could fractionate submicrometer solutes to high purity at high process capacity. However, a number of obstacles, in particular the stability of the carrier flow and the solute. path lines, may hinder development of this rotor. This paper describes the principles underlying the design and operation of a hybrid rotor, as well as some of the problems that will have to be resolved before this technology can be reduced to practice.