Aurein 1.2 is a small cationic antimicrobial peptide, one of the shortest peptides that can exert antimicrobial activity at low micromolar concentrations. Aurein 1.2 is a surface acting peptide, following the "carpet" mechanism of thresholded membrane disruption. It is generally assumed that the activity of such cationic α-helical membrane disrupting peptides is charge driven. Here, the authors show that instead of charge interactions, aromatic phenylalanine residues of the Aurein 1.2 sequence facilitate the membrane binding. The activity of the wild type peptide was compared to mutants in which the Phe residues were substituted, singly and in tandem, with alanine. Measurements by quartz crystal microbalance, impedance spectroscopy, and dye leakage experiments demonstrated that single residue mutants retain a much-reduced activity whereas the deletion of both Phe residues prevents membrane disruption entirely. The single residue mutants exhibited an altered mechanism of action, permeabilizing but not dissolving the target membranes. These results offer a new design rule for membrane disrupting peptides with potential pharmacological applications.