The role of connective tissue in facilitating and directing the growth of epithelia during adult life is uncertain. The basic processes associated with maintenance of epithelial structure and previous work concerning the role of mesenchyme in this process in the embryo and adult are reviewed. A series of experiments examining the role of connective tissue in facilitating epithelial growth and development in vitro and after transplantation in vivo is described, These confirm the requirement for dermal elements if normal structure is to be reestablished and point to the requirement of dermal, as opposed to deep, connective tissues for facilitation of the growth of adult epithelia in vivo, The in vitro experiments suggest the presence of diffusible dermally produced factors that facilitate epithelial growth.