An in vitro model for partial-thickness cutaneous wound healing is described in which the influence of variables present in vivo, such as blood-borne factors and inflammatory cells, is eliminated. Dermal sheets of porcine skin are maintained in culture at the air-liquid interface in serum-free medium, and re-epithelialization from the keratinocytes of the hair infundibula can be studied. Dermal sheets of different thicknesses harvested from various depths were first evaluated for viability and regenerative potential in serum-supplemented medium. Mid-dermal explants, 20/1000 inch thick, showed the greatest epithelial outgrowth from the appendigeal keratinocytes and the longest viability in vitro. Explants of this type were used in all subsequent experiments. The effects of growth factors on re-epithelialization of the explants were studied in a serum-free environment. Epidermal growth factor, cholera toxin, bombesin, and insulin-like growth factor alone and in various combinations were applied to the explant surface in aqueous solutions by micropipette. Outgrowth was assessed by computerized morphometric analysis (RS/1 program by BBN) at days four and eight. Among all factors tested, cholera toxin alone and in combination with insulin-like growth factor produced the greatest epithelial outgrowth. Nevertheless, topical applications of growth factors failed to induce complete re-epithelialization within the experimental time frame. In contrast, explants to which cultured human keratinocyte sheets were topically applied regenerated a confluent and regularly stratified epidermis within 6 d.