PTMA (prothymosin, alpha, N-GST chimera) is a small, 12.4 kDa protein. It is a 109-111 amino acid long polypeptide as the precursor of thymosin a1. Thymosins are named becaues they were originally isolated from the thymus. But now in many other tissues, thymosins also can be detected. Thymosins have diverse biological activities, and two in particular, thymosins a1 and _4, have potentially important uses in medicine, some of which have already progressed from the laboratory to the clinic. In general, PTMA is associated with cellular proliferation and carcinogenesis (Eschenfeldt et al., 1986), cellular and viral transcription (Cotter et al., 2000), protection against apoptosis and chromatin remodelling (Karetsou et al., 1998). PTMA may have a dual role both intracellulary and extracellulary. In relation to diseases, thymosins have been categorized as biological response modifiers. Thymosin a1 is derived from PTMA. For animals that lack thymus glands, thymosin a1 is responsible for the activity of that preparation in restoring immune function.