Intradiffusion coefficients of iron(II) and water were determined in acidified solutions of iron(II) perchlorate for an iron concentration range of 0 to 2.5 mol-dm-3 at 25°C. In addition ancillary shear viscosity and density data were measured for each solution. Results were compared with existing diffusion data for iron(III) perchlorate solutions and highlighted the differences in the solvent dynamics around the two metal ions. By use of a simple model the effective hydration of the iron(II) ion was estimated to be 12, comparable to that of other divalent, uncomplexed metal cations; the same model indicates an effective hydration of 19 for iron(III). © 1992 Plenum Publishing Corporation.