There are disclosed .beta.-sheet mimetics and methods relating to the same for imparting or stabilizing the .beta.-sheet structure of a peptide, protein or molecule. In one aspect, .beta.-sheet mimetics are disclosed having utility as protease inhibitors in general and, more specifically, as serine protease inhibitors such as thrombin, elastase and Factor X inhibitors. In one embodiment, the .beta.-sheet mimetic is a thrombin inhibitor.