Low-dose endometrial after loading irradiation was used in 19 mentally retarded women for the induction of therapeutic amenorrhea. They were divided into two subgroups on the basis of age: 13 young patients (mean age 17 years, range 13-26 years) and six patients of middle age (mean age 42 years, range 34-44 years). In the young patients, during the 10-month follow-up period, the plasma E2 levels did not decrease. However, the FSH concentration increased. Late on, 2-9 years after treatment, the E2 levels were significantly higher than those of healthy postmenopausal women and did not differ from the values of healthy women in the sixth to seventh days of the menstrual cycle. At that time the FSH and LH levels were similar to reference values in reproductive age. The E2/E1 ratio was significantly higher than that of healthy women in the sixth to seventh days of the cycle and that of postmenopausal women. Most of the menstrual cycles were anovulatory but some ovulatory also occurred. The testosterone concentrations did not differ from reference values. The ovaries of the middle age patients were more sensitive to irradiation than those of the younger patients.