Prostaglandin inhibitors may be a viable alternative to the currently available hormonal contraceptive methods. Hormonal contraception, although highly effective, is not tolerated by some women, and contraindicated in others. Hormonal emergency contraception works primarily by inhibition of ovulation, and therefore fails in women who use the method after release of the oocyte. Studies have shown that prostaglandins appear to play a critical role in ovulation and maintenance of the corpus luteum. Thus their inhibition may prevent ovulation and provide contraception prior to fertilization and implantation, or prevent implantation and pregnancy by causing premature luteolysis (ovulation failure). Whether one or both of these effects occurs in women is unknown. Obtaining data on the effect of a prostaglandin inhibitor on cycle length is particularly relevant for their further development as a potential contraceptive. If these agents affect luteolysis, then this will lead to premature menstruation rendering them not acceptable as an ongoing daily method of contraception. However, premature luteolysis could provide a mechanism for emergency contraception that would provide superior protection than the currently available forms of hormonal emergency contraception since protection against pregnancy would occur even after ovulation. As an initial step toward understanding the potential contraceptive effects of prostaglandin inhibitors, we propose to test the hypothesis that the use of a prostaglandin inhibitor will result in premature luteolysis (ovulation failure) in women.