Benzyloxycarbonyl peptide p-nitrophenyl esters have been prepared by the mixed carbonic anhydride method using amino acid or peptide p-nitrophenyl esters as amino components. Removal of the N-protecting group produces higher peptide active esters, which can then be used either in a further peptide coupling reaction with a benzyloxycarbonyl amino acid, or polymerized to form sequential polypeptides. The advantages and limitations of the procedure are discussed.