The hydrodynamics and residence time distribution (RTD) of two microreactors based on the split-and-recombination (SAR), and multilamination mixing mechanisms, respectively were investigated. It was found that the design of the distribution manifolds of the SAR mechanism produces an unbalanced flow distribution. For feeding ratios different than one, bypassing and recirculation occur within the SAR manifolds. For equal flow rates the SAR flow behavior can be accurately described by the pure convection model. The manifold used in the multilamination microreactor achieves a homogeneous distribution of flow and its interdigital mixing structure generates an alternated pattern of fluid layers which is maintained for Re 140. After this point the ordered arrangement is broken and two large segregated zones are formed. In the absence of molecular diffusion both microreactors reach limiting values of scale and intensity of segregation that were found to be independent of the energy applied to the system. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 988-1001, 2013