The technique of post-coital ligation and transection of the oviducts from the uterus has been used to establish the rate of transport of a vanguard of competent spermatozoa at two stages of oestrus in 30 ewes. Whereas 20% of eggs were fertilized when this procedure was performed 8h after mating at the onset of oestrus, 94% of eggs were fertilized when the transection was performed 8h after mating on the second day of oestrus (P<0·01) . The latter matings were regarded as peri-ovulatory, and indicate that the rate of sperm transport is influenced by ovarian activity. Roles for follicular steroid hormones, prostaglandins and relaxin are discussed, as is a local route of transfer of these hormones to the wall of the oviduct.