Technique for the characterization and preparation of subcellular particles. A sucrose gradient is used to fill a centrifuge tube of the type swinging-bucket design. The bottom is the most dense, and the top the least dense. The solution is then layered with a suspension of the particles. Centrifugation separates particles in the gradient according their density. The centrifugation is over. After that, the bottom of the tube with sucrose particles of equal density drips into a series receiving tubes.