Although it is known that glycosaminoglycans (GAG) can affect hair growth, their role in follicular growth regulation is not yet understood. We have administered one such GAG, heparin, to anagen-induced mice to help to elucidate this role, using the C57 Bl-6 model for murine hair growth studies. Heparin was found to exert dose- and hair cycle-dependent, differential effects on skin epithelial cell functions. Intraperitoneal, but not topical application of heparin inhibited the development of anagen follicles in anagen-induced mice as assessed by morphometry. When the skin of heparin-treated mice was cultured in an organ culture assay, the epidermis showed a significant increase in the synthesis of arginine-rich proteins (ARP), while epithelial bulb, but not epidermal cell proliferation was reduced in comparison with control skin. In mouse-skin organ culture, the effects of direct administration of heparin to the medium on epithelial cell proliferation and ARP synthesis were dose-dependent and varied (inhibition or stimulation of either parameter), depending on the stage of the hair cycle, the cell population in question (epidermal vs. epithelial bulb keratinocytes), and the length of incubation. PAM cell and mouse dermal papilla cell proliferation in vitro was inhibited by heparin. We conclude that heparin may be a useful tool for characterizing the role of GAG in epithelial cell biology and epithelial-mesenchymal interactions in general, and in hair growth in particular.