The hydrodynamic study of a three-phase airlift reactor with an enlarged head zone was carried out. Effects of gas-solid-liquid separator design and riser to downcomer cross-sectional area using different lengths and diameters of the draft tube were investigated. Ca-alginate beads with entrapped yeast biomass at different loadings up to 21 % (v/v) were used in order to mimic the solid phase of conventional high cell density systems. The main hydrodynamic parameters - liquid circulation velocity, gas and solids holdups in all reactor sections have been measured and experimental values were satisfactorily predicted using an appropriate three-phase model. The results of this study may be applied to suggest the optimal design (in terms of hydrodynamic behaviour) of a batch/continuous three-phase ALR for high cell density fermentations.