Vitamin A has been said to have an antikerat-inizing effect on human and animal epidermis by either topical or systemic administration. Evidence, however, is conflicting (Fisher and Herrmann (1)). Our purpose was to analyze the action of high oral doses of vitamin A on the mitotic activity induced in human epidermis by tape stripping (2). It was pointed out in a previous publication (Hunter, Pinkus, and Steele (3)) that the stripped off keratin cells can be counted accurately, and quantitative data obtained in this respect before and after administration of vitamin TABLE I Keratin cells per square cm of skin surface before vitamin A, after one month of 150,000 units of Vitamin A, and one month after discontinuing Vitamin A 6 Sex Control One Month :tion Change Two Months :tion Change Case P 1 F 1,718,400 739,200 - 660,800 - 2 M 1,395,200 1,017,600 - 2,376,000 + + 3 M 1,360,000 995,200 - 1,161,600 + 4 F 1,328,000 516,800 - 2,233,600 + + 5 M 1,156,800 715,200 - 812,800 + 6 M 1,116,800 809,600 - 856,000 + 7 M 1,094,400 868,800 - 1,288,000 + + 8 M 1,084,800 814,400 - 787,200 - 9 M 1,060,800 766,400 ~ 644,800 - 10 F 856,000 772,800 - 1,028,800 + + A are reported here. Data on mitotic activity and other changes in the living cells of the epidermis will be reported later. Ten adult volunteers were used. An area on the flexor surface of the forearm was denuded of its keratin layer by repeated application of Scotch Tape® until a glistening surface was obtained. A similar procedure was performed on a new area after the subject had taken a dose of 150,000 units of synthetic vitamin A daily for 30 days. This was administered in the form of buccal tablets for intra-oral absorption.1 Otherwise the subjects ate ad libitum. A third area was stripped a month later when the subjects had been on an unrestricted diet without vitamin supplement. Keratin cells from each procedure were counted according to the method described (3) by pooling the cells from squares of tape (}£ inch sidelength) representing identical areas of skin surface. Fig. 1. Number of keratin cells in 10 volunteers after one month of therapy and one month after discontinuing Vitamin A, expressed as per cent of control value. Counts expressed as cells per square cm are listed in Table I. It can be seen that counts were depressed at the end of the experimental period in all ten subjects. They ranged from 39 to 90% of the control figures (Fig. 1). At the end of the second period there was great variability of response. Counts were further depressed in 3 subjects, rose slightly in 3 others, but remained below the original 1 Vi-Dom-A® Oral Tabs were supplied by Dome Chemicals Inc. of New York City. 459 460 THE JOURNAL OF INVESTIGATIVE DERMATOLOGY figures, and rose above the control count in the remaining four. In two of these the final counts were 168 and 170% of the control figure. It has been shown previously that the accuracy of the counting procedure is good, the results are reproducible, and repeat counts on the same subjects vary only within narrow limits. Variations of more than 15% can be considered significant. SUMMARY Oral administration of 150,000 units of vitamn A daily for one month decreased epidermal keratin cell counts significantly in nine out of ten normal volunteers. One month after discontinuation of therapy a variable pattern was found, ranging from slight additional depression to values far exceeding the control counts.