Twelve patients with 16 leg ulcers, existing for at least 3 months and not responsive to conventional inpatient therapy of at least 3 weeks, were treated with repeated applications of cultured allogenic keratinocyte sheets. A marked decrease in size was seen in all ulcers but 2. Complete closure of the ulcer was seen in 62% of the ulcers within 8 weeks. Healing was due to enhanced granulation and increased epithelialization, starting from the periphery of the wound. This edge effect suggests that the epidermal allografts act by stimulation of migration and/or multiplication of the acceptor's keratinocytes, rather than by take of the allograft.