[en] Diffusion of ¹⁴⁴Ce³⁺, ²⁴¹Am³⁺ and ²³⁹Pu⁴⁺ has been investigated in a polymetacrylic acid type ion-exchange resin and in a heterogeneous, sulphuric acid type membrane, with microautoradiographic method. The concentration distribution and the activation energy of diffusion have been determined. The results plotted in lg c/c₀-X² coordinates have formed straight lines. The possible error of diffusion coefficients determined from the slopes is +-20%. The values are independent of diffusion time within the range of the experimental errors. (K.A.)