Cultured keratinocyte grafting (KG) of chronic leg ulcers produces an impressive stimulation of host epithelization by an effect on the edge of the ulcer, which starts to grow in rapidly ("edge effect"). In 5 patients with chronic leg ulcers treated by KG, we have studied the proliferation index of the epidermis of the edge and of the graft area and that of secondary culture keratinocytes. The aim of the study was to correlate this parameter with the clinical evolution of the treated lesions. We found a significant correlation between the proliferation index of the edge epidermis and the clinical evidence of "edge effect".