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Three model peptides of different sizes (17-24 amino acid residues), mimicking the chymotrypsin inhibitor SCGI (a peptide of 35 amino acid residues) isolated from Schistocerca gregaria were designed and prepared by convergent peptide synthesis. Selective formation of disulphide bridges in the closing step was achieved without selective protection of cysteine residues. The natural pattern of the two disulphide bridges was determined by 2D homonuclear H-1 NMR techniques. All three model peptides were characterized by amino acid analysis, MS and CD spectra. Preliminary results revealed that the two smaller model peptides exhibit no inhibitory activity, whereas the larger one shows limited inhibition of chymotrypsin. Copyright 2002 European Peptide Society and John Wiley Sons, Ltd.