Peptide libraries were simultaneously synthesized on single supports by double coupling 0.8 equivalents of an equimolar acylating amino acid mixture consisting of 19 amino acids (cysteine omitted) at randomized sites, thus compensating for the different coupling rates of the amino acids. Peptide epitope mixtures, as well as very complex mixtures such as a completely randomized hexapeptide, were prepared and analyzed by HPLC and amino acid analysis. The results obtained indicate that this method can be applied to the synthesis of peptide libraries. Parts of a simultaneously synthesized solution phase combinatorial library XXB1B2XX were successfully used for the detection of the linear epitope HFND of transforming growth factor-alpha (TGF alpha) recognized by the monoclonal antibody Tab2. Furthermore, novel combinatorial peptide libraries XXB1B2XX were prepared on continuous cellulose membrane supports, also allowing the identification of TGF alpha epitope sequences. In addition, peptide mixtures that bound to a double-stranded DNA (15mer) and silver were identified. These preliminary results indicate that cellulose-bound combinatorial peptide libraries can be used for the rapid and inexpensive screening of millions of peptides to identify single molecules that bind any given ligand such as proteins, nucleic acids and metals.