Thymocartin (also known as T4 and RGH-0206) is a protected synthetic tetrapeptide patented by Hungarian multinational pharmaceutical and biotechnology company Gedeon Richter Plc. (Richter, Gedeon, Vegyeszeti Gyar Rt) as an immunomodulating agent. In preclinical models, Thymocartin shows to exert similar immunomodulatory activities to thymopoietin affecting both humoral and cellular responses. In skin graft mouse model Thymocartin increases the number of splenic T cells and restored the rejection capacity of thymectomized C57Bl mice. In chronic 28-days i.v. toxicity studies in dogs no adverse reaction has been found. The low toxicity of Thymocartin is probably attributable to their short half-life as the half-life of the Thymocartin is less than 3 min in humans.