The sensitivity of Langmuir-Blodgett (LB) films of the co-ordination polymer poly(CuMBSH) to organic vapours has been investigated using electrical impedance spectroscopy. The films were exposed to benzene, ethanol, acetonitrile and water vapours. In all cases, a reversible change in the capacitance and conductance of the LB film was observed. The effects of water vapour are shown to be different from those observed with the organic vapours.