Iron oxide particles were precipitated in Nafion(R) 117 perfluorinated ion-exchange membranes using four different methods. Precipitated ferrites yielded magnetically responsive nanocomposite films and probed structural variations in the membrane. Optical microscopy, transmission electron microscopy, vibrating sample magnetometry (VSM), and Mossbauer spectroscopy were used to characterize the materials. Microscopy showed that the ferrites were distributed unevenly across the films with a dense skin making up the surface layers. Higher temperature enhanced accessibility to iron and increased ferrite loadings were obtained for these samples. Nanosize particles of magnetite (Fe3O4) were present as disks or as clusters of disks in all the treated films. Needles and bundles of needles of maghemite (gamma-Fe2O3) were produced in the films that were reacted at the boil. All the samples exhibited superparamagnetic response by VSM. Due to the shorter time scale of the Mossbauer measurement (similar to 10(-7) s), ferrimagnetic response was detected for boiled and autoclaved samples.