The use of the iodide-iodate test reaction was extended to study micromixing in glycerin-water mixtures with viscosities up to 170 mPas. The properties of the mixtures and the kinetics of the test reaction were determined as a function of viscosity. Experiments were carried out in a stirred tank yielding the micromixedness ratio alpha = (1-X-s)/X-s as a function of stirring speed for different viscosities. A micromixing model involving two steps (incorporation of bulk fluid and exchange between smaller eddies) has been used for the interpretation of the experimental data. Further work is required to interpret experiments at higher viscosities where hydrodynamic data are still lacking.