The early immune response in alopecia areata is characterized by a Th1 T helper cell cytokine pattern and an aberrant expression of ICAM-1 and HLA-DR molecules on lesional hair bulbs. A counteracting cytokine pattern induced by a therapeutic contact dermatitis is supposed to mediate the hair regrowth. In addition to cytokines, growth factors have been shown to influence immune responses, and we therefore investigated the expression levels for a panel of growth factors in untreated versus alopecia areata after treatment with the contact sensitizer diphenylcyclopropenone. Using semiquantitative reverse transcriptase polymerase chain reaction we detected a striking overexpression of transforming growth factor beta 1 mRNA in successfully treated patients. This cytokine has been shown to be a potent immune response modifier, which can suppress Th1 immune responses. The way in which topical immunotherapy induces hair regrowth in alopecia areata is unknown, but a lesional increased expression of transforming growth factor beta 1 may be a possible mechanism.