The anti-fertility activity of prostaglandin synthesis inhibitors namely the non-steroidal anti-inflammatory drugs: acetyl salicylic acid, indomethacin and oxyphenbutazone were investigated in male and female albino rats and female albino rabbits. Oxyphenbutazone and indomethacin affected the reproductive process in male rats. Indomethacin 3 mg/kg. and acetyl salicylic acid 300 mg/kg produced significant anti-ovulatory activity in the rabbit. In female rats, all three drugs given in high doses over a period of two oestrous cycles reduced mating significantly, while only indomethacin given in a low dose of 0.8 mg/kg over a period of six oestrous cycles could reduce mating significantly. Anti-implantation activity was seen with indomethacin 4 mg/kg. alone, and though post-implantation activity was seen with all three drugs, it was associated with maternal deaths. It appears that non-steroidal anti-inflammatory drugs affect reproduction in female animals.