Peptides that consist of 19 residues with random sequences (X19) were considered to deliver antigenic stimuli to CD4T cells. When IL-4, IL-7, IL-9, IL-15 and agonistic Ab to CD29 were co-cultured with single peripheral CD4T cells in the presence of X19 and feeder cells, T cells exhibited clonal expansion. These T cell clones showed heterogeneous proliferation patterns against KGXXXXXXXXXGK-based and KGXXXXXXXXXGKGKK-based combinatorial peptide libraries. Pattern-match search on one of the T cell clones resulted in peptide ligand candidates, one of which induced proliferation, as did protein molecules carrying the corresponding sequence. Combinatorial chemistry was useful in determining not only peptide ligands but also peptide superagonists. For this purpose, use of reverse-phase hydrophobic interaction chromatography and mass spectrometry analysis was efficient. Detailed methods are described in the paper.