Thirty years ago, Lagües and Domange  studied surface segregation kinetics and proposed a method by which it is possible to determine the equilibrium surface segregation isotherm from one measurement, supposing that the local equilibrium hypothesis (LEH) is obeyed. This method has been using widely in the literature (e.g. [2-4]) since its born. It was used e.g. to study of dissolution of thin films into different substrates. In this case additionally it was assumed that the kinetics can be described by the classical Fick I equation (hybrid method). In this paper, using computer simulations, we investigate that under which conditions the LEH is obeyed during the dissolution of a thin film. Moreover, we show that even when the LEH is fulfilled the proposed ‘hybrid’ method cannot be always applied. We make also some considerations on the effect of stress fields developed by the redistribution of the solute elements during the segregation kinetics.