Results are reported for the repeated reduction of iron oxide particles. 300-425 mu m diameter, by a mixture of CO, CO2, and N-2 in a fluidized bed of 20 mm internal diameter. The conclusions were as follows: (1) Reduction of either Fe2O3 to Fe3O4 or of Fe3O4 to Fe0.947O is first-order in CO. (2) With the particle sizes used, the rates of the reduction reactions are controlled by intrinsic chemical kinetics. Activation energies and pre-exponential factors are reported. (3) The first cycle gave anomalous results, but (a) the rate of reduction of Fe2O3 to Fe3O4 remained constant over cycles 2-10; (b) the rate of reduction of Fe3O4 to Fe0.947O declined by 60-85% over cycles 2-10. (4) The rates of reduction declined with solids conversion down to zero at 80% conversion. The rates were incorporated into a conventional model of a fixed bed, which was used to predict, satisfactorily, the reduction behavior of iron oxide. (C) 2009 American Institute of Chemical Engineers AIChE J, 56: 1016-1029, 2010