Single spermatozoa and spermatozoa in rouleaux were found throughout the genital tract of 21 female guinea pigs killed 15 minutes to 24 hours after copulation. Three females killed three to five minutes postcopulation had single spermatozoa and spermatozoa in rouleaux in the vagini, cervix, and uterus but not in the oviduct. The number of rouleaux and the number of spermatozoa in individual rouleaux decreased after copulation in all parts of the female genital tract with time while a corresponding increase in single spermatozoa was evident. The rate of rouleaux dissociation was faster in uteri than in oviducts. Only single spermatozoa were found near ova in the oviducts. The uterotubal junction appeared to act as a barrier to multitudes of spermatozoa passing from the uterus to the oviducts. However, some single spermatozoa and some rouleaux passed this barrier. Unusually large rouleaux were observed up to 12 hours after copulation in the pockets of the uterotubal junction. Single spermatozoa and few rouleaux of two spermatozoa in the uteri of females killed 8 to 24 hours postcopulation were phagocytised. No phagocytosis of spermatozoa was observed at any time in the oviduct.