The complex of bioelectrical paramenters (membrane potential, membrane resistance and capacitance) of internodal cells of Nitellopsis obtusa was measured over a wide range of IAA concentration (10−10 to 10−4M) with two intracellular microelectrodes. Primary effects of IAA at a concentration as low as 10−10M were observed. The optimum range of IAA action was from 10−9 to 10−6M. The type of IAA-induced electroresponse depended on the initial level of membrane potential, which characterized the energetic state of the plasmalemma. In the energized state (ca −200 mV) N. obtusa cells appeared to have 3 typical reactions: hyperpolarization (membrane potential less than K+-equilibrium potential), depolarization (membrane potential higher than K+-potential) and absence of response at K+-electrochemical equilibrium. Membrane capacitance was found constant at 0.74 ± 0.05 μF cm−2, but membrane resistance increased up to 50% independently of the sign of the electrogenic reaction. Increase of membrance capacitance and decrease of the membrane resistance was a feature of the de-energized state (ca −135 mV) and may be explained by lower viscosity of membrane lipids, which interacted with IAA. The complex of parameter, including cytoplasmic steaming taken as an indicator of energy supply, is discussed as indicating slow IAA penetration combined with a primary action of IAA on the plasmalemma receptor sites.