The effect of the homologous series of 1,1-dialkylpiperidinium bromides on the potassium leakage from Escherichia coli cells has been studied. The minimum concentration for each compound which is able to release maximum of cellular potassium has been determined and correlated with the inhibitory activities of the compounds. The relationship between the structure and the activity enables to consider the K+ leakage as the marker of inhibitory activity of the membrane active antimicrobials.