A randomized, double-blind, group-comparative study was performed over a 6 month period to compare ovarian suppression and vaginal bleeding during the use of three oral contraceptives containing doses of 30, 50 or 75 micrograms desogestrel. A total of 44 female volunteers with regular cycles and established ovulation by ultrasonography were recruited from an out-patient clinic in a university hospital and asked to participate in the study. Ultrasonography and serum oestradiol and progesterone measurements were performed during two assessment periods. The 75 microgram dose showed complete suppression of ovulation and a more acceptable bleeding pattern than the lower doses. The 75 microgram dose of desogestrel is the most promising dose for the development of a new progestogen-only oral contraceptive agent.