A process for adhering polyethylene to aluminum was developed which involves treating the aluminium substrate successively with chromic acid and then a selected organic acid. Certain organic acids utilized in this process appeared to produce a synergistic effect on the adhesion. This process, which required no modification or treatment of the polymer, resulted in peel strengths forty times greater than that obtained on untreated aluminum. Tensile shear values for the polyethylene–aluminum bond were greater than 2800 psi. The materials used for treating the metal in this system produced a maximum in the obtainable peel strength. Furthermore, minor changes in the etching acids resulted in drastic changes in the adhesion values.