Eight postclimacteric women were given 80 mg polyestriol phosphate by intramuscular injection in order to analyse the effect of the drug on the vaginal cytology. In four patients, whose vaginal smears showed complete atrophy before treatment, a clear but weak oestrogen effect was observed after the medication. This effect appeared after one week in three patients and after two weeks in one patient, and it lasted four weeks in three cases and two weeks in one. In four patients, whose vaginal smears showed a weak oestrogen effect before treatment, the therapy did not result in any significant change of the vaginal smear pattern.