Nonathymulin (Thymulin, FTS) is well defined nonapeptide hormone produced by thymic epithelial cells. Its biological activity and antigenicity depend upon the presence of the metal zinc in the molecule. Thymulin consists of a biologically inactive nonapeptide component termed FTS (anacronym for serum thymus factor in French) coupled in an equimolecular ratio to the ion zinc, which confers biological activity to the molecule. This pharmacologically active metallopeptide induces the differentiation of T-cells and enhances several functions of the various T-cell subsets in normal or partially thymus-deficient recipients. The peptide is a natural hormone, available in synthetic form. Thymulin has a selective immunomodulatory effect, enhancing anti-inflammatory and inhibiting pro-inflammatory cytokines. It suppresses p38 (implicated in glucocorticoid-resistance) and inhibits NF-kappaB activation, which has an important pathogenic role in several lung diseases. The broad spectrum of anti-inflammatory effects of this peptide in several animal models of lung disease makes thymulin a good candidate for future clinical trials. Thymulin was being investigated by Santen Pharmaceutical in Japan. Its development for the treatment of ischaemic heart disorders and rheumatoid arthritis in Japan was discontinued. Thymulin is probably the best characterized of all putative thymic hormones and seems to playa physiological role in thymus–pituitary communication, particularly during perinatal life. Interest in the therapeutic use of thymulin flourished during the 1970s and 1980s when efforts were almost exclusively focused on using thymulin for the treatment of autoimmune and other immunopathologies as well as cancer. Subsequent studies established that thymulin is active on the hypophysis and the brain. This awareness and the availability of a synthetic gene for metFTS have opened new avenues for the exploration and eventual exploitation of the therapeutic potential of this metallopeptide.