The purpose of this paper is to report histologic and clinical observations at intervals up to four years, following both therapeutic and experimental abrasion of the skin. Material and Methods Thirteen patients from the Dermatology Service (Surgical Skin Planing Clinic) of the Los Angeles County General Hospital and from the private practice of one of us (S. A.) were utilized in this study. Some were relatively young, with acne scars of the face (the biopsy specimens included skin not acne scarred, however), while the majority were in the 70- to 80-year age bracket with multiple recurrent actinic keratoses of the face (farmers' or sailors' skin). In the case of two men whose backs were utilized for quantitative studies, the skin was normal senile skin. The abrasions were performed with a motordriven rotating abrasive instrument. A steel wire brush18 was used on the earlier patients and