A no-moving-part microfluidic oscillator was developed for mixing two reactants prior to their admission into a microreactor. Instead of the spatial periodicity produced by static mixers, it achieves essentially the same resultant effect by temporal periodicity. In one half of the oscillation period the oscillator directs into its output one reactant, followed by the other reactant during the other half-period. Since the periods are short, the flow in the output channel consists, like in the static mixers, of interleaved layers of the two fluids - here, however, oriented perpendicularly relative to the flow direction. The oscillation depends on dynamic effects so that there is a lower limit of Reynolds numbers at which the device can operate. In experiments this limit was at Re similar to 30, which makes the device well suited for use with present-day microreactors, especially if the mixer is used to supply several reactors in parallel. Data from experiments with two different models agree with very simple kinematic theory for oscillation frequency and for the size of the generated layers in the output. (C) 2009 Elsevier B.V. All rights reserved.