Human keratinocytes were cultured on an inert polymeric film support in serum-free medium to produce subconfluent autologous skin grafts for healing of burn wounds and chronic leg ulcers, The growth of keratinocytes in Petriperm with such a hydrophilic film bottom as a culture support was superior to that in T-flask offing to better cell adhesion. Based on this principle, an autonomous modular bioreactor, KERATOR for large scale production of skin grafts up to 5280 cm(2) in size was constructed. It is computer controlled, and operations such as cell seeding and medium change are automated. The cell growth rate profiles in the bioreactor and Petriperm are similar, evincing the significance of KERATOR, The harvested skin grafts consist of the polymeric film covered by subconfluent sheets of non-differentiated keratinocyte cells. Such grafts may be applied to wounds in "upside-down" fashion.