Thymosin Beta 4 is a naturally occurring peptide. It is found in high concentrations in blood platelets, wound fluid and other tissues in the body. Tβ4 is not a growth factor; rather, it is a major actin regulating peptide. Tβ4 has been found to play an important role in protection, regeneration and remodeling of injured or damaged tissues. The gene for Tβ4 has also been found to be one of the first to be upregulated after a wound occurs.

NMR structure of a β-thymosin. Both thymosin α₁ ^[1] and β-thymosins are intrinsically unstructured proteins, i.e. they lack a stable fold when free in aqueous solution. This structure, mostly alpha helix, was artificially stabilised by an organic solvent.^[2] The thymosin illustrated, originally named β₉ is the cow orthologue of human β₁₀