Scanning electrochemical microscopy (SECM), in the substrate generation-tip collection (SG-TC) mode, has been used to detect the cuprous ion Cu-(aq)(+) intermediate formed during the course of electrodeposition of Cu metal from aqueous CuSO4 solution. Addition of chloride is confirmed to strongly stabilize the Cu-(aq)(+) ion in aqueous solution and enhance the rate of Cu electrodeposition. This SECM method in the SG-TC mode offers an alternative to the rotating ring disk electrode (RRDE) technique for in situ studies on the effect of plating bath additives in metal electrodeposition. An attractive feature of the SECM relative to the RRDE method is that it allows qualitative aspects of the electrodeposition process to be studied in close proximity to the substrate in a simple and direct fashion using an inexpensive probe, and without the need for forced convection. (C) 2008 The Electrochemical Society.