Clean and well-ordered Au(111) and Pt(111) electrodes were prepared in a UHV chamber, transferred to an electrochemical cell by a closed-transfer system and immersed in 0.1 M HClO4 at various potentials. From the charge flowing during contact with the electrolyte under potential control, the potential of zero charge (pzc) was derived. Au(111) was used as a test system and very good agreement was obtained between the pzc values determined by in-situ capacity measurements in dilute solutions and by the immersion technique. For Pt(111) the pzc was found to be very positive, within the oxide region, and hence not directly accessible by experiment. However, from charge measurements in the double layer region, the pzc of Pt(111) could be estimated to lie around 0.9 V vs. Ag/AgCl.