The oxygen diffusion and exchange behaviour of Nd1+zBa2-zCu3Oy has been studied by analysing the reaction between the 123 phase and an O-18 enriched gas phase. The oxygen mobility and isotope exchange activity of the cuprate depend on the number of vacancies in the CuO2-layers and the BET surface area of Nd1+zBa2-zCu3Oy but not on the Nd/Ba ratio (z = 0, 0.1 and 0.2) of the solid solutions. It has been established that characteristic diffusion data (T-onset, diffusion rate etc.) are more sensitive to changes in the measuring conditions or in the properties of the samples than the results observed for the isotope exchange reactions.