The method is made understandable by the figure. A 27-member peptide library is synthesized from three amino acids. After the first (A) and second (B) cycles samples were set aside before mixing them. The products of the third cycle (C) are cleaved down before mixing then are tested for activity. Suppose the group labeled by + sign is active. All members have the red amino acid at the last coupling position (CP). Consequently, the active member also has the red amino acid at the last CP. Then the red amino acid is coupled to the three samples set aside after the second cycle (B) to get samples D. After cleaving, the three E samples are formed. If after testing the sample marked by + is the active one it shows that the blue amino acid occupies the second CP in the active component. Then to the three A samples first the blue then the red amino acid is coupled (F) then tested again after cleaving (G). If the + component proves to be active, the sequence of the active component is determined and shown in H.