Electrochem. anodic oxidn. of aluminum metal sheets leads to the formation of compact and dense, but highly porous alumina surfaces on top of the anode. The alumina surfaces obtained by anodic oxidn. can be detached from the bare metal by using a voltage detachment procedure, without employing chem. etching techniques. This procedure leads to large area porous alumina membranes with closed backsides. Prestructuring of the aluminum base metal leads to ordered pore regions at anodization voltages of 25, 40 and 50 V, resulting in porous alumina membranes with pore diams. of 33, 40 and 72 nm. The careful opening of the backside alumina membranes can be realized by acid treatment leading to highly flexible large area porous alumina membranes with complete through-hole pore morphol. The backside pore-opening process realized by chem. etching is strongly dependent on time and acid concn. and is best monitored routinely by microscopy techniques in order to gain control over the process.