The self-assembly technique was used to prepare polymeric thin films composed of bilayers of polypyrrole (PPY) doped with different counter-ions and poly(3-thiophene acetic acid) (PTAA), directly on conducting glass electrodes. The electrical conductivity of these thin films - which have a relative high degree of structural order and large surface to volume ratio - responds in a very fast manner to the exposure to vapors of simple organic solvents (methanol, ethanol, carbon tetrachloride and benzene). The changes in the fractional difference of individual films disposed as an sensor array were measured and the Principal Components Analysis (PCA) was used to correlate the corresponding collective pattern to the specific volatile compound.