['To design, develop and validate a new device allowing the features of corneocytes at the surface of the skin to be visualized in vivo and objectively characterized.', 'Monochromatic light is focused at the proximal end of a coherent bundle of optical fibres. Fluorescence of skin, stained with fluorescein, is then captured by the same fibre bundle and displayed, through a dichroic mirror, by a CCD camera. Fluorescence images are analysed using dedicated software to measure the projected area of cells.', 'The new device allows the mean projected area of corneocytes to be routinely studied and quantified on most of the skin areas of the human body. Measurements carried out on two age groups of women confirm that corneocyte size on the forearm is smaller in young women than in older women.'] Does a new technique to in vivo study the corneocyte feature at the surface of the skin?