The design and synthesis of 13 novel peptidyl carbamates are described. When tested for inhibitory activity toward porcine pancreatic elastase, trypsin, and chymotrypsin, six compounds were found to specifically inhibit elastase without affecting the other two serine proteases. All the active inhibitors had an amino acid isostere at the P1 position. Kinetic studies indicated that the inhibition was competitive with Ki values ranging from 4.23 X 10(-5) to 2.4 X 10(-6) M. The degree of inhibition was found to be dependent on the specificity of the peptide chain for the extended subsites on the enzyme as well as on the nature of P1'. Preliminary work on one inhibitor indicates that the inhibition is reversible and proceeds via the rapid formation of a strong enzyme-inhibitor complex, followed by slow acylation of the serine residue on the active site of the enzyme. Peptidyl carbamates represent a novel class of elastase inhibitors.