There is increasing interest in nanostructures and in the molecular design of building blocks which self-assemble into nanoscaled intelligent materials. We outline a method for controlling the nanostructures of amphiphilic nonapeptides by changing the pH of the aqueous medium. A lysine residue on the hydrophilic face of the peptide plays a critical role as a morphology-control unit. This self-assembling peptide may, therefore, find application as a template for peptide-directed biomineralization.