Development of high-speed countercurrent chromatography requires basic knowledge of hydrodynamic behavior of the two-phase solvent system.  With several types of the horizontal flow-through coil planet centrifuge devices, motion and distribution of two immiscible solvent phases in coiled columns were studied under various experimental conditions.  Results obtained with fifteen different types of commonly used solvent systems were summarized below: 1) Under a proper mode of synchronous planetary motion, the two solvent phases are unilaterally distributed in the rotating coil with one phase (head phase) on the head side and the other phase (tail phase) on the tail side.  2) Three solvent groups classified according to the hydrophobicity of the non-aqueous phase display the characteristic hydrodynamic trend: In the hydrophobic solvent group the upper phase becomes the head phase, while in the hydrophilic solvent group the lower phase becomes the head phase.  In the intermediate solvent group, the head phase is determined by a parameter beta which is the ratio of the coil radius to the orbital radius of the column holder.  3) The above hydrodynamic trend of the solvent system is most closely correlated to viscosity of the solvent system so that raising the temperature results in drastic change of the hydrodynamic trend of the hydrodaynamic trend of the solvent system especially in viscous butanol solvent systems.  4) Stroboscopic observation of the colored solvent phases revealed that each coiled turn contains mixing and settling zones, each zone traveling toward the had end of the coil at a rate of the revolution speed of the coil.  This indicates that solutes present in the coil are subjected to a repetitive mixing and settling process in the coil at an enormously high rate of over 13 times a second which explains the high partition efficiency produced by high-speed countercurrent chromatography.