We have studied the gas sensing properties of five polyaniline-based materials thick and thin PANI films, nanocomposite PANI/MWNT and PANI/SWNT films, and PANI nanogranules embedded in a polyvinylpyrrolidone matrix. The films (except for the latter) were deposited within the induction period of the polymerization process on gold interdigitated micro electrodes. Their sensitivity to NH(3), H(2), ethanol, methanol, and acetone was measured. The thin PANI film (similar to 100 nm thick) prepared by a lift-off process had the sensitivity to ammonia below 0.5 ppm, which was higher than that of nanocomposite films. Two materials-thick PANI film and nanocomposite PANI/MWNT film exhibited a shallow minimum in the temperature dependence of resistance (at 313 K and 319 K), which is a feature exploitable in practical applications, since the gas sensors should be insensitive to small temperature fluctuations at these temperatures. (C) 2011 Elsevier B.V. All rights reserved.