We attempted to establish a coculture model of human dermal papilla cells (DPCs) from androgenetic alopecia (AGA) and keratinocytes (KCs) to study the pathomechanism of AGA. Since expression of mRNA for the androgen receptor (AR) decreased during subcultivation of DPCs in vitro, we transiently transfected the AR expression vector into the DPCs and cocultured them with KCs. In this coculture, androgen inhibited the growth of KCs by 50%, indicating that the DPCs produce diffusible growth suppressive factors into the medium in an androgen-dependent manner. Since recently increasing evidence has shown the importance of transforming growth factor-β1 (TGF-β1) in hair growth, we further examined the concentration of TGF-β1 in this coculture medium after androgen treatment by ELISA assays. The results showed that androgen treatment increased the secretion of TGF-β1 into the conditioned medium. Moreover, neutralizing anti-TGF-β1 antibody reversed the inhibition of KC proliferation. Thus, we suggest that androgen-inducible TGF-β1 derived from DPCs mediates hair growth suppression in AGA.