An intervention trial using oral oestriol to treat urinary incontinence was performed in a number of patients taken from a representative sample of 562 women aged 75 yr. The clinical series consisted of 34 patients who took part in a double-blind crossover study of the possible effects of oestriol, given in a single daily dose of 3 mg, and of a placebo over a period of 3 mth. The clinical examinations included bacteriological cultures and an assessment of the degree of atrophy of the surface membranes in the vagina. In most patients, oestriol was effective in reversing the atrophy. The clinical effect was excellent in urgency and mixed incontinence, but not in stress incontinence