A method for single cell DNA measurements by flow cytometry based on a technique successfully used for the hamster cheek pouch epithelium was extended for studies on human epidermis. A least squares estimation procedure was used for the statistical analysis of the initially obtained DNA frequency distribution. In 14 specimens of abdominal skin from a young healthy female the precentages of epidermal cells with an S-phase DNA content were 3.0 +/- 0.6 (SD), and the percentages of epidermal cells with a G2+M phase DNA content 1.1 +/- 0.1 (SD). No significant differences in values were found for specimens investigated in different experiments. No influence of tissue storage time for a maximum of 32 days in liquid nitrogen was discernible. Values from the corresponding dermal tissue were significantly more variable then the epidermal values, but the levels were of the same magnitude. It is concluded that this technique used for human epidermis yields sufficient stable and accurate estimates of S and G2+M fractions that it should be a valuable tool useful as an alternative or a supplement to conventional cell kinetic methods.