The diffusion-evaporation method, developed several years ago by Kofstad is shortly discussed with the background of experimental results obtained on the Mn-MnS system from evaporation kinetics and radioactive tracer experiments. Excellent agreement between self-diffusion coefficients of cations in Mn1+yS determined experimentally and those calculated from evaporation rate measurements clearly indicates that this novel fascinating method can successfully be utilized in studying the transport properties of transition metal oxides and sulphides in equilibrium with the metallic phase. A notable feature of this method is that diffusional transport is studied under carbon- (and hydrogen-) free conditions, while in conventional, much more difficult, tracer experiments CO-CO2 or H-2 - H2O (H-2-H2S) gas mixtures must be used in order to obtain such low oxidant activities.