Residence time distribution of solids in single and multicompartment fluidized beds was investigated as a function of solids and gas flow rates. Two types of baffles were investigated-perforated plates and plates equipped with a downcomer. The residence time distribution was represented by the F function and was determined experimentally with the aid of a pulse of magnetic tracer. The residence time distribution for a single stage was represented by [formula omitted]. The two parameters, η and ε, varied as would be expected from the physical behavior of the system. The results obtained for multistage operation could be calculated by the use of the values obtained for η and ε from single-stage data.