The synthesis and in vitro enzyme inhibition profile of a series of novel trifluoromethylketone (TFMK) inhibitors of human plasma kallikrein (PK) are described. We have developed an efficient method for the construction of peptide TFMKs that provides the final product devoid of compromised stereochemical integrity. Many of these compounds are potent inhibitors of PK and exhibit reduced inhibition of tissue kallikrein (TK) and plasmin (HP).