On a basis of results obtained from experimental investigation of distribution of local rates during electrochemical micromachining in presence of photoresist masks under various hydrodynamic conditions (macroscopically non-uniform rotating disk electrode, sprayer, electrode in the cell with chaotic electrolyte mixing) we demonstrated in all three cases under these hydrodynamic conditions maximum localization is reached when the rate of ionic mass-transfer controls the rate of dissolution (when anodic limiting current are achieved). In presence of closed turbulent vortices in the area of undercutting and turbulent flowing round the etch localization increases in comparison with localization provided by geometric parameters of mask (primary current distribution). These conditions (the control of electrochemical reaction by the rate of ionic mass-transfer, the presence of closed turbulent vortices in the area of undercutting) are necessary to develop methods to increase localization by pulse anodic-cathodic machining.