Local anaesthetic carbisocaine decreased the electrical conductivity of gramicidin channels in planar lipid membrane made from bovine brain total lipids in n-hexane at the concentration (1.6 +/- 1.3) X 10(-5) mol/l, which is similar to that found to block propagation of action potential on the sciatic nerve. To study the mechanism of this effect the authors investigated the disordering effect of carbisocaine on rat total lipid membranes at the 5th, 12th and the 16th carbon membrane depths, using ESR spectroscopy of spin-labelled stearic acids. Carbisocaine disorders the membrane and the effect increases towards the methyl terminal of the lipid acyl chains. It is suggested that carbisocaine-induced perturbation of the membrane may have a secondary influence on the conductivity of gramicidin channels in the membrane.