SUMMARY The oestrogenic activity of the phenolic fraction of human urine has been measured by its effect on vaginal smears from spayed mice and compared with that of its contained oestrone, oestradiol-17β, and oestriol as determined chemically by the method of Brown [1955]. Eleven urine samples, collected from normal women during the menstrual cycle and pregnancy and after the menopause, from normal men and from a eunuch have been tested. In all but one of the samples there was satisfactory agreement between the biological and chemical results. It is concluded that the chemical method adequately measures the oestrogenic activity in the phenolic extract of normal urine.