This paper deals with the prediction of the impeller speed required for complete suspension of solid particles. Based on the inspection analysis of the governing equations, the dimensionless equation expressing such impeller speed was proposed. The specific forms of this equation were determined experimentally for a six-pitched blade turbine for solid concentrations of 2.5 and 10% by volume. Four different hydrodynamic regimes were observed depending on the relative particle size and Reynolds number values. In view of our results the weaknesses of existing theories and correlations were shown and discussed.