We have investigated thein vitrorefolding process of human proinsulin (HPI) and an artificial mini-C derivative of HPI (porcine insulin precursor, PIP), and found that they have significantly different disulfide-formation and PIP differ in their amino acid sequences due to the presence of the C-peptide linker found in HPI, therefore suggesting that the C-peptide linker may be responsible for the observed difference in folding behaviour.