Langmuir film formation was investigated in a series of alkylheteroaromatic compounds and their mixtures. In the case of pure amphiphilic molecules, the shape and nature of the hydrophilic group seems to play a decisive role in the film formation; however, in binary systems a positive synergy was observed allowing to obtain two-component film of reasonable quality even if one or both the components separately manifested moderate or weak ability for film formation. Compression and deposition of mixtures of poly( 3-n-alkylthiophenes) with suitable builders is described. The thicknesses of the binary LB films, determined from the measurements of tile surface plasmon resonance, are controlled by the packing of the film builder. The optical and electrical properties of the Langmuir-Blodgett films are modified by the presence of nitrogen oxides. The overall effect is probably due to two competing processes : doping of the polymer and an irreversible reaction destroying the conjugated chain.