Two alternative expressions exist for the diffusive flux in inhomogeneous systems: Fick's law and the Fokker–Planck law. Here the origin of these expressions was re-examined and numerical and physical experiments were performed in order to shed light on this duality. It was concluded that, in general, the Fokker–Planck expression should be given preference, in spite of the fact that Fick’s law was more popular.On the Applicability of Fick’s Law to Diffusion in Inhomogeneous Systems. B.P.van Milligen, P.D.Bons, B.A.Carreras, R.Sánchez: European Journal of Physics, 2005, 26[5], 913-25