AbstractBecause the human immunodeficiency virus type 1 protease (HIV‐1‐PR) is an essential enzyme in the viral life cycle, its inhibition can control AIDS. The folding of single‐domain proteins, like each of the monomers forming the HIV‐1‐PR homodimer, is controlled by local elementary structures (LES, folding units stabilized by strongly interacting, highly conserved, as a rule hydrophobic, amino acids). These LES have evolved over myriad generations to recognize and strongly attract each other, so as to make the protein fold fast and be stable in its native conformation. Consequently, peptides displaying a sequence identical to those segments of the monomers associated with LES are expected to act as competitive inhibitors and thus destabilize the native structure of the enzyme. These inhibitors are unlikely to lead to escape mutants as they bind to the protease monomers through highly conserved amino acids, which play an essential role in the folding process. The properties of one of the most promising inhibitors of the folding of the HIV‐1‐PR monomers found among these peptides are demonstrated with the help of spectrophotometric assays and circular dichroism spectroscopy. Proteins 2006. © 2005 Wiley‐Liss, Inc.