Abstract The properties are studied of a fluidized bed composed of two dissimilar materials differing greatly in particle size and density. The two-component system consists of ceramic rods suspended in a fluidized bed of zircon sand. The distribution and motion of the rods is studied with the aid of a cylindrical bed-container which is built up of perspex rings. It is concluded that the time needed to obtain a stationary distribution of rods is less than 1 minute, and that there is intensive mixing of the rods, except in the region just above the distribution plate. The maximum concentration of rods at which they all remain suspended in the fluidized bed is found to be considerably lower than that which might be expected for a homogeneous mixture of the components.