Ovulation induced by HCG in rabbits was blocked by a single subcutaneous injection of 6 mg/kg indomethacin given 6 h after the insemination and HCG treatment. In addition, a time-dependent inhibition in the fertilization rate after indomethacin treatment was also recorded. This suggests that indomethacin, when given at a critical time and at an appropriate dose level, not only blocks ovulation but also interferes with fertilization. Treatment with graded amounts of prostaglandin-F2 alpha incorporated in a Silastic-polyvinylpyrrolidone-gel (PVP) had marginal to no effect after intravaginal placement on 4- or 6-day pregnancy. However, 5 mg PGF 2 alpha/ Silastic-PVP tube when placed intravaginally on Day-7 of pregnancy resulted in termination of pregnancy in 66% of the treated does. This implies that young corpora lutea are resistant of PGF2 alpha treatment and that pregnancy at the time of ovo-implantation can be terminated by PGF2 alpha incorporated in a Silastic-PVP tube.