The technique of a.c. impedance spectroscopy is used to investigate biomembrane Langmuir-Blodgett (LB) films deposited on platinum electrodes. The characterization of the uncoated electrode system is first of all described. Measurements of the complex admittance of a multilayer of 22-tricosenoic acid are then presented. The results show that the specific resistance and inverse capacitance of the multilayer vary linearly with the number of layers. Two valinomycin-containing mixed LB film systems were also examined. When these systems were immersed in KCl electrolytes, the expected changes in film conductance were not observed. Possible explanations for the lack of a potassium response are proposed.