Thymosin beta 4 is a small 43-amino-acid molecule that has multiple biological activities, including promotion of cell migration angiogenesis, cell survival, protease production, and wound healing. We have found that thymosin beta 4 promotes hair growth in various rat and mice models including a transgenic thymosin beta 4 overexpressing mouse. We have also determined the mechanism by which thymosin beta 4 acts to promote hair growth by examining its effects on follicle stem cell growth, migration, differentiation, and protease production.