the present invention is directed to the use of thymohexin the linear peptide ARG-ASP-LYS-VAL-TYR-ARG, as a therapeutic agent for the prophylaxis and/or treatment of autoimmune diseases, cancer infectious diseases, inflammatory diseases, and neurodegenerative diseases. Moreover the present invention relates to pharmaceutical compositions preferabley in form of lyophilisate, liquid solutions, liquid buffer solutions, semi-solid or solid forms containing thymohexin optionally together with at least one pharmaceutically acceptable carrier, cryoprotectant, lyoprotectant, excipient and/or diluent.