Stimulus-responsive peptide self-assembly provides a powerful method for controlling self-assembly as a function of environment. The development of a reductive trigger for peptide self-assembly and subsequent hydrogelation is described herein. A self-assembling peptide sequence, Ac-C(FKFE)(2)CG-NH2, was cyclized via disulfide bonding of the flanking cysteine residues. The macrocyclic form of this peptide enforces a conformational restraint that prevents adoption of the beta-sheet conformation that is required for self-assembly. Upon reduction of this disulfide bond, the peptide relaxes into the preferred beta-sheet conformation, and immediate self-assembly into fibrillar superstructures occurs. At sufficient peptide concentration, self-assembly is accompanied by the formation of rigid, viscoelastic hydrogels.