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. Positional scanning Positional scanning was introduced independently by Furka et al. and Pinilla et al. The method is based on the synthesis and testing of series of sublibraries. in which a certain sequence position is occupied by the same amino acid. The figure shows the nine sublibraries (B1-D3) of a full peptide trimer library (A) made from three amino acids. In sublibraries there is a position which is occupied by the same amino acid in all components. In the synthesis of a sublibrary the support is not divided and only one amino acid is coupled to the whole sample. As a result one position is really occupied by the same amino acid in all components. For example in the B2 sublibrary position 2 is occupied by the „yellow” amino acid in all the nine components. If in a screening test this sublibrary gives positive answer it means that position 2 in the active peptide is also occupied by the „yellow” amino acid. The amino acid sequence can be determined by testing all the nine (or sometime less) sublibraries. Omission libraries In omission libraries a certain amino acid is missing from all peptides of the mixture. The figure shows the full library and the three omission libraries. At the top the omitted amino acids are shown. If the omission library gives a negative test the omitted amino acid is present in the active component. Deconvolution of tethered combinatorial libraries If the peptides are not cleaved from the solid support we deal with a mixture of beads, each bead containing a single peptide. Smith and his colleagues showed earlier that peptides could be tested in tethered form, too. This approach was also used in screening peptide libraries. The tethered peptide library was tested with a