The present work applies the methodology proposed by Parise er al. [M.R. Parise, O.P. Taranto, P.R.G. Kurka, L.B. Benetti, detection of the minimum gas velocity region using Gaussian spectral pressure distribution in a gas-solid fluidized bed, Powder Technol. 182 (2008) 453-458], as an alternative to the spectral analysis of pressure fluctuation measurements to find the region where the minimum velocity gas takes place in a gas-solid fluidized bed, that is, the zone where the bed is tending to defluidization. The technique is applied to analyze the effect of fixed bed height and particle density in defluidization conditions for particles of microcrystalline Cellulose and sand. Tests are carried out for three fixed bed heights (0.15, 0.20 and 0.25 m) and two particle densities (980 and 2650 kg/m(3)). Experiments show that the best conditions for identifying the defluidization zone are obtained with lower bed aspect ratios (H/D) and lower particle density. The results indicate the high potential of the proposed method for industrial applications, especially for on-line control of gas-solid fluidized bed processes where the defluidization phenomenon needs to be detected and avoided, (C) 2008 Elsevier B.V. All rights reserved.