Electrical and morphological properties of neat iron- and iron oxide-filled multi-walled carbon nanotubes and its dispersion with a semiconducting polymer were investigated. The electrical properties of these carbon nanotubes changed significantly when exposed to different atmospheres. The current voltage characteristics of the films formed from the dispersions were obtained from planar devices with metallic electrodes. These devices were used as gas sensor and as memory devices where the writing, reading and erasing can be done electrically. (C) 2007 Elsevier B.V. All rights reserved.