Diffusion coefficients of dioxygen in aqueous KCl, LiCl and MgCl2 solutions were determined by means of polarography at 25 degrees C. The concentration ranges covered up to 3 mol dm(-3) for KCl, 10 mol dm(-3) for LiCl and 3.5 mol dm(-3) for MgCl2. The diffusion coefficient decreased with the salt concentration, rather moderately in KCl but rapidly in the other cases. The Walden products remained relatively constant up to ca. 5 mol dm(-3) in all cases, but increased in LiCl solutions at higher concentrations. In LiCl and MgCl2 solutions the diffusion coefficient of dioxygen and the self-diffusion coefficient of water were almost the same over the whole concentration range.