Two once-a-month injectable contraceptive formulations, HRP112 (depot-medroxyprogesterone acetate, 25mg and estradiol cypionate, 5mg.) and HRP102 (norethisterone enantate, 50 mg and estradiol valerate, 5 mg,) were compared in two groups of women witn regard to effectiveness, reported complaints and reasons for discontinuation. A total of 2328 women were recruited into a seventeen-centre, randomized clinical trial. Follow-up was for a period of one year and resulted in a total of 10,969 women-months of experience of HRP112 and 10,608 women-months of experience with HRP102. The study showed little difference in efficacy and side-effects between the two formulations. Two pregnancies occurred in women receiving HRP102, giving a cumulative life-table pregnancy rate at 12 months of 0.18 per 100 woman-years. None occurred in the group receiving HRP112. There was no difference in the overall continuation rates between the two groups at one year, being 64.5% in the HRP112 group and 63.2% in the HRP102 group. The rates for all medical and non-medical reasons given for discontinuation were comparable between the two treatment groups. Discontinuations for bleeding irregularities were low, being 6.3% and 7.5% for HRP112 and HRP102 respectively, as well as for 'amenorrhea', the respective figures being 2.1% and 1.6%. There were, however, marked centre-to-centre differences. Both products were shown to be highly effective contraceptive preparations, which gave rise to few discontinuations due to menstrual cycle disturbances when compared witn progestogen-only injectable contraceptives. As such it is expected that they will have an important role in family planning programmes in many countries throughout the world.