Abstract Side effects of the insecticide lindane on plant cells are not well understood. To get more information about this problem, effects of sublethal doses of lindane on the membrane potential of the submerged macrophytic fresh-water plant Elodea densa were studied. Using standard intracellular microelectrode techniques, membrane potential levels and time-courses in intact and lindane-treated leaves were investigated in light and in darkness. Lindane produced a time-dependent inhibition of light-induced membrane potential changes. More than 10 hr application of 10 ppm lindane (effective concentration) resulted in a complete insensitivity of the membrane potential to illumination. The basis of this effect is not quite clear, but several possibilities are discussed. On the other hand effects of lindane on the diffusion membrane potential were studied. Lindane decreased the level of the diffusion potential. Additionally, the voltage responses of the diffusion potential to rapid changes in the potassium/sodium relation of the outer solution were found to be lowered drastically by lindane. These results suggest a direct interaction of lindane with the plasmalemma, resulting in a loss of the potassium/sodium selectivity. The findings indicate that biomembranes appear to be a favored target of lindane action in living plant cells.