The mixing and segregation behavior of spherical solids between 20 and 40 min in diameter in a bubbling fluidized bed of quartz sand was investigated. The experimental system used is a cold-air fluidized bed of 0.45 X 0.45 in bed area and about 0.5 rn bed height. Binary systems "particle/sand" were studied using two different sizes of sand (Geldart B-D) and varying the fluidization velocity and the size, density and volumetric fraction of the large solids. Time average segregation patterns of the solid mixtures were obtained from single particle trajectories measured by a newly developed experimental procedure. The method utilizes the interactions between a magnetic field imposed on the fluidized bed chamber and a single metal covered tracer particle, which is moving inside the fluidized bed. The technique proposed is generally suitable to locate metallic spheres in three dimensions inside non-transparent and non-metallic media at rates of about 50 samples per second. Experimental results presented within this paper indicate that segregation of large flotsam particles is apparent in bubbling fluidized bed systems particularly at low superficial velocities, in coarse particle systems and for low densities of the flotsam particles.