It is demonstrated experimentally by example of simple, commercially available T-junctions and by ''unsymmetrical'' V-type micromixers that mixing times cannot be derived by applying the Iodide Iodate Reaction Method without considering the specific mixer geometry. Experimental results differ depending on the orientation of the feeds with respect to the inlets. An explanation for the observed effects is suggested. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 835-840, 2011