Platelet-derived growth factor (PDGF) is a potent mitogenic factor for many cell types and has been shown to be important in follicular development and vasculogenesis. In this study, we examined the expression pattern of both PDGF factors and their corresponding receptors in mesenchyme-derived dermal papilla cells (DPCs) and epithelial follicular keratinocytes (FKs). Both types of PDGF receptors are expressed in FKs, whereas DPCs only express PDGF receptor beta on the protein level, a finding also seen in whole organ cultures. By examining the expression of PDGF ligands, we were able to show that cultured FKs synthesize both PDGF-A and PDGF-B, whereas, DPCs only express PDGF-A. As immunomodulatory cytokines were shown to affect hair growth, we investigated the effects of IL-1beta, IL-4, TNF-alpha, TGF-beta and IFN-gamma on the expression levels of PDGF factors in cultured DPCs and FKs. Interestingly, we could show a significant down-regulatory effect by catagen-inducing cytokines like IL-1beta or IFN-gamma, suggesting a possible involvement of PDGF signaling in the induction of catagen. The question concerning the latter hypothesis remains to be elucidated in further studies on whole organ cultures.