Impedance spectra in the range from 10 Hz to 1 MHz were obtained for apples for temperatures between 4 and 40 degrees C. At each temperature the measured spectrum was fitted to a theoretical model in which the bulk properties of the apple were represented as the parallel combination of a constant phase element and a resistance. The results were used to determine the activation enthalpies of apples for ionic migration, H-m, and for dissociation of an ion from its binding site, H-f. H-m was found to be of the order of 0.15 eV whereas H-f was of the order of 0.03 eV. Changes in the slope of the activation curves indicated that a structural change occurred in the cell wall within the temperature range between 35 degrees C and 40 degrees C.