Scale-up rules for liquid-liquid dispersions in stirred tank have been discussed. Multifractal model of turbulence was used to interpret the scale effect on drop break-up and coalescence rates for drops of low and high viscosity. It has been shown that for equal power input per unit mass and geometric similarity of the agitated vessel, viscous and inviscid drops break faster at large scale. It has been also shown that drops with partially mobile interfaces coalesce faster in large-scale systems, while behaviour of drops with immobile interfaces depends on their deformation. Coalescence rate of small rigid droplets decreases with the increase of tank scale, whereas larger deformed drops coalesce faster in larger scale tanks. It was also shown that coalescence of rigid drops takes place mainly in the impeller zone, while deformed drops with partially mobile and immobile interfaces coalesce in the bulk. The best scale-up results are expected for = const., t(cir) = const. and D/T not equal const. (c) 2004 Elsevier Ltd. All rights reserved.