The healing of full thickness surgical wounds from 0 to 14 days has been studied in hairless mice. Within 2 days after wounding the surrounding epidermis is thickened and primarily composed of enlarged basophilic cells. The remnants of the hair follicles attached to the epidermis are converted into cords of enlarged basophilic cells. Epidermal thickening is maximum at 7 days. Associated with the epidermal thickening surrounding the wound edge is an increase in the total number of cells in the stratum granulosum and in the stratum spinosum. The number of basal cells does not change. Mitotic activity and mitotic rate increase within 1 day after wounding. Both reach their peaks by approximately 5 to 7 days and then begin to return to control levels. Mitotic duration does not change.