Detailed information about the electrochemical and physicochemical phenomena associated with copper nanowire growth within the nanosized pores of polycarbonate track-etched membranes (PCM) was in situ obtained by electrochemical impedance spectroscopy. From an equivalent circuit that reproduces the ac-impedance results, it was found that the charge-transfer resistances associated with the Cu2+ -> Cu+ and Cu+ -> Cu degrees electrochemical processes presented low and high values, respectively. It was also possible to observe the change from a diffusional growth process inside the pores (first stages) to a growth process in solution (film formation onto PCM). (c) 2007 The Electrochemical Society.