Specific correlations for mass transfer in transition and turbulent flows close to a rotating disk have been established by means of local measurements. A circular Pt microelectrode (⊘ 80 μ) was mounted flush with the Pt disk electrode (⊘ 10 cm) and insulated from it by a very thin epoxy ring gap (breadth ∼ 10 μ). Both the disk and the microelectrode were polarized in the conditions of the diffusion plateau corresponding to the fast reduction of the ferricyanide ion and the currents measured for each electrode. The microelectrode current thus yields the local density of the diffusional flux over the disk electrode. The measurements performed in a large range of Reynolds (Re) and Schmidt (Sc) numbers showed that the flux of diffusion is proportional in transition flow to Sc1/3 Re5 and in turbulent flow to Sc1/3 Re0.91. The relationship obtained for the eddy diffusivity was DT/V = 4.45 10−4 y+ 3.