A novel experimental approach to the investigation of the repertoire of peripheral T lymphocytes of patients suffering from ankylosing spondylitis (AS) is proposed. This approach is based on the wide-range sequencing of cDNA of the β-chain of the T-cellular receptor (TcR). The results of the analysis of the diversity of sequences of the TcR antigen-binding domain (CDR3) inside the total pool of one patient with AS are presented by the example of the second V family (BV2) of TcR. The expansion of six independent TcR-expressing clones of T cells with a similar amino acid sequence of the CDR3 domains was proposed based on the results of the comparative structural analysis of the clone libraries of the cDNA of TcR BV2. The long-time stable expansion of these T clones was demonstrated during the development of the disease by specific monitoring. © 2010 Pleiades Publishing, Ltd.