This work is focused on the investigation of coalescence under shear flow in aqueous mixtures of Na-alginate and Na-caseinate. Shear flow was generated in a parallel plate apparatus coupled with an optical microscope. Drop size distribution was measured as a function of time by computer controlled 3D optical sectioning of the sample and offline image analysis. Automated procedures of image analysis, based on out-of-focus components subtraction and drop contour detection, were implemented to measure a large number of drops, as required to minimize sampling errors. The effects of dispersed phase volume fraction and shear rate on the flow-induced evolution of the drop size distribution were explored. Finally, 3D reconstruction of the locations of the drops within the sample was performed to evaluate possible wall and sedimentation effects. (C) 2004 Elsevier Ltd. All rights reserved.