Solid circulation patterns were, determined by measuring collisions between tracer particles and cylindrical probes in liquid-solid and gas-liquid-solid fluidized beds. Special probe's were used to two- and three-dimensional views of particle, motion. Circulation patterns for 3 and 5 mm glass beads were studied.-Mixing cells, which had - been formed at low liquid velocities, grew in size and eventually merged as the liquid velocity increased. The flow patterns of smaller particles having the same density as bed particles and particles lighter than bed particles (graphite particles) with the same size were also measured.