The gas sensing ability of electrochemically prepared pure polyaniline and polyaniline-poly(bisphenol-A carbonate) films is investigated. The responses of the composite films to several vapours are more well defined and reproducible compared to the pure conducting polymer. The changes in resistance as determined via the two-probe technique are well defined down to a level of 0.025% vol./vol. ammonia. The possible reason for such a difference is discussed. The structure of the composite is examined through pyrolysis FT-IR studies.