Toluene vapour sensing has been successfully demonstrated using Langmuir-Blodgett films prepared from substituted phthalocyanines, containing copper or nickel as the central metal ions. High-quality layers have been built-up and the films characterised using surface plasmon resonance (SPR). Exposure to toluene resulted in a partially reversible shift in the resonance depth and position of the SPR curves. The optical sensor could detect concentrations of this organic vapour down to, at least, 50 parts per million.