The chemical synthesis of peptides and proteins is described and the use of the synthetic approach to answer various biological questions is discussed. The plan was to assemble a peptide chain in a stepwise manner while it was attached at one end to a solid support. With the growing chain covalently anchored to an insoluble matrix at all stages of the synthesis, the peptide would also be completely insoluble and, furthermore, would be in a suitable physical form to permit rapid filtration and washing after completion of each of the synthetic reactions. The intermediate peptides in the synthesis would thus be purified by a very simple, rapid procedure rather than by the usual tedious crystallization methods.