NuvaRing, a novel contraceptive vaginal ring, releases 15 microgram of ethinylestradiol (EE) and 120 microgram etonogestrel (ENG) per day. A randomized pharmacokinetic study compared NuvaRing with a combined oral contraceptive (COC) containing 30 microgram EE and 150 microgram desogestrel. Maximum levels of EE and ENG with NuvaRing were 30% and 40%, respectively, of those seen with the COC. Because ENG bioavailability was higher following vaginal administration, the systemic progestogen exposures were comparable with the two contraceptives. However, the EE bioavailabilities were similar with both routes and so EE exposure with NuvaRing was half that with the COC. Pharmacodynamic studies have examined ovarian function during recommended and altered NuvaRing use. The use of NuvaRing for the recommended 3-week period completely inhibited ovulation. During an additional 2 weeks of use, ovulation continued to be inhibited. Early NuvaRing removal after just 3 days had no effect on the time to ovulation compared with recommended use, thus indicating that 3 days of use seem to be sufficient to suppress ovarian activity. Finally, delayed ring insertion (when the follicles had developed to 13 mm) resulted in inhibition of ovulation in all women. In conclusion, NuvaRing effectively inhibits ovulation during recommended and altered use, showing that it is a robust contraceptive method.