Current-controlled voltage (i-v) characteristics of a membrane produced from a block copolypeptide of L-glutamic acid and L-leucine were studied in solutions with various pHs and salt (KCl, NaCl) concentrations. Though ohmic behavior was observed at pH 3.5, at higher pHs the i-v curves were sigmoidal and hysteresis occurred. When the scan speed of the current was decreased, the hysteresis disappeared but the sigmoidal shape still remained. Membrane resistance increased from one step to the next with increasing current. Though the shape of the i-v curve in the NaCl solution system was very similar to that in the KCl solution system under the same experimental conditions, the membrane resistance in the NaCl solution system was larger than that in the KCl solution system. The existence of two resistance states in the membrane is discussed in relation to the molecular conformation (alpha-helix and random-coil structures) of the poly(L-glutamic acid) block chain.