In this paper we report on the corrosion behavior of Ti3GeC2 and Ti2AlN in a 1 M NaOH solution, investigated by electrochemical impedance spectroscopy (EIS), polarization, and zeta-potential measurements. The EIS results for Ti3GeC2 and some results for Ti2AlN could be fitted to a complex equivalent circuit, where the double layer is represented by a constant phase element. The passive film is represented by a polarization resistance in series with a parallel connection of a resistance of the passive film (R-pf) and its capacitance (C-pf). In both cases passive layers were formed. Based on the zeta-potential measurements, we conclude that the passivating layer that forms on Ti3GeC2, over a wide pH range, is most likely GeO2-based, while the one formed on Ti2AlN is most likely Al2O3-based and/or TiO2-based. (c) 2006 The Electrochemical Society.