A levonorgestrel-releasing intracervical device (ICD) was inserted postmenstrually to twenty-one voluntary women. Eight subjects gave blood samples twice a week during the initial three months of use of the ICD and during the seventh and twelfth months of use. Clinical performance was studied; plasma concentrations of levonorgestrel were measured by radioimmunoassay and the effects of the treatment on pituitary and ovarian function were determined by assaying plasma concentrations of LH, FSH, estradiol and progesterone. The results of the first year are presented. Dysmenorrhea, menstrual flow and the number of days of bleeding decreased during the first treatment year. Three spontaneous expulsions occurred; two at the very beginning of the treatment and one after six months of use. Side-effects were few. The plasma level of levonorgestrel remained fairly constant during the observation time of 12 months. Thirty-one of the 36 cycles were ovulatory as judged by plasma progesterone elevations. No pregnancies occurred during the study period of one year.