The minimum fluidization velocity of beds has been determined experimentally in beds of 0.089 m and 0.29 m diameters, respectively. The particles studied had sizes ranging from 100 mum to 1 mm in diameter, and densities from 1128 to 11400 kg/m(3). Three distributors were used in the experimental scheme, each perforated by holes of 0.8 mm in diameter but with varying hole densities, as well as a porous plate. It was found that the minimum fluidization velocity was affected by both the diameter and distributor used. The effect of vertical tubular inserts on the minimum fluidization velocity was investigated in the 0.29 m diameter bed. The experimental data in the large bed, using four distributors, were parameterized within experimental error.