An experiment is described that enables the statistical stability of the Preisach diagram for interacting ferromagnetic particles to be tested. The samples used were of &ggr;—Fe2O3dispersed in a nonferromagnetic matrix to a nominal packing density of 20% by volume. Both oriented and nonoriented samples were examined. In every case the diagram was found to be stable over most of the area bounded by the major remanence loop. The region of departure from stability occurred at the higher levels of remanent intensity. A method of calculating the diagrams using only dc measurements is given. They are then used to predict accurately the ascending remanence curve after ac demagnetization for each sample. Finally, it is shown how the experimental ascending and descending remanence curves, which could not be explained by Wohlfarth's relations [J. Appl. Phys.29, 595 (1958)] based on noninteracting particles, can be completely described in terms of the Preisach diagram.