Poly(n-butyl methacrylate) (PBMA)-polyaniline (PANI) composite films were obtained by extrusion by use of two methods: the first method consisted of polymerizing a thin layer of PANI, with Cl- as dopant, on the extruded film of PBMA; the second method was based on blends of PBMA and PANI produced by the extrusion of the two polymers by using dodecylbenzene sulfonic acid (DBSA) as dopant. The thermal properties, electrical conductivity, and morphology of the composite films obtained were measured. The sensitivity of the composites films as detectors of hydrogen peroxide and ammonia was evaluated. The change in the electrical resistance on exposure to different aqueous solutions of these components shows a linear behavior. (C) 2003 Wiley Periodicals, Inc.