Abstract: A method of preparing cyclic peptide mixtures via side chain or backbone and solid phase synthesis. The cyclic peptide mixtures form libraries that are useful for screening purposes featuring the attachment of an amino acid to a solid support through its side chain or backbone in order to mimic solution cyclization procedures with linear peptides. In the preferred embodiment, Boc chemistry is used for peptide synthesis, wherein the initial attachment of a trifunctional amino acid is by the aspartyl side chain (with OFm for alpha-carboxyl protection). Cyclization is performed using uronium reagents with racemization suppressant, and a strong acid (HF) is used for deprotection and cleavage. The strategy has been used for the preparation of a series of cyclic peptide mixtures. The procedure is expandable to include at least twenty different amino acids at each position (except the resin linked position where most attachments are by Asp, Lys, Glu, or Orn).