Abstract 1. 1. Indomethacin (Id) treatment of rabbits at the time of implantation resulted in a significant reduction in the number of viable embryos as well as a significant reduction in plasma progesterone concentrations. 2. 2. Treatment with a mixture of prostaglandins (PGs) together with Id caused a significant increase in both the number of viable embryos and in plasma progesterone concentrations when compared to the treatment with Id alone. 3. 3. The PG mixture used in the present study did not succeed in fully reversing the Id antifertility effect.