A porous copper residue has been produced by the selective dissolution of aluminium from CuAl2into aqueous alkali solution at 1°C and 93°C. The residue was examined by replica and thin-foil microscopy and found to consist of cylindrical single-crystal copper rods or fibres of very uniform diameter. The fibres were curved but aligned with their average direction approximately parallel to the direction of the de-alloying reaction. The fibres produced by leaching at 93°C were spaced at approximately 110nm intervals, whereas those produced at 1°C were spaced at about 40 nm. All observations are shown to be in accord with a cellular phase transformation model for the de-alloying reaction.