Ovariectomized, oestrogen-primed rabbits were injected intravenously with varying doses of oxytocin immediately after insemination with a standardized inseminate. The does were killed 30 min after insemination and the number of spermatozoa in different segments of the genital tract was determined. The most significant finding was that when 80 mu. oxytocin were given, mass transport of semen into the uterus occurred. This suggests a coordinated response of the genital tract to a critical oxytocin stimulus which facilitates mass transcervical passage of fluids. However, when 80 mu. oxytocin were given to intact oestrous rabbits, no significant effect on sperm transport was detected.