The paper presents the results of corrosion behaviour of brass-118 in artificial seawater and the inhibitor effect of benzotriazole (BTA) by using a novel method called dynamic electrochemical impedance spectroscopy (DEIS). This method allows the tracing of the dynamics of the corrosion and the inhibition process based on the evaluation of electrical parameters of the equivalent circuit. Instantaneous impedance spectra recorded up to 10 h show that an exposure of few hours is not enough for the determination of inhibition efficiency. The results indicate the usefulness of DEIS technique in the field of inhibitor research.