Three-dimensional chemical syntheses of proteins have been developed for the total synthesis of insulin-like molecules (insulin, relaxin, and bombyxin). The method used peptide synthesis in combination with a site-directed formation of one intrachain and two interchain disulfide bonds. Although the disulfide synthesis occurs under denaturation conditions the proteins were fully biological active. In order to investigate the structure-function relationship of these hormones a variety of defined analogs were synthesized including insulin derivatives which were not obtainable by the commonly used chain-combination method. This implies that site-directed disulfide formation could be a method of choice to produce small disulfide rich proteins.