Spermatozoa were recovered from the uterine horns or vagina of mated rabbit does 12-20 hr p.c. and their fertilizing capacity tested in an in-vitro system. Uterine spermatozoa gave consistently high fertilization (93-100%) throughout. Vaginal spermatozoa gave good results (81-85%) 12-14 hr p.c. but fertilization then declined with time. Vaginal spermatozoa recovered from mated females with or without ligation of the uterine horns were equally able to fertilize eggs. Fragmentation of uncleaved eggs was noted in experiments with vaginal spermatozoa, but never with uterine spermatozoa. The former were slower in penetrating eggs and the zygotes were correspondingly slower in cleaving. Triploidy, possibly due to ageing, was found in approximately 15% of the embryos fertilized by vaginal spermatozoa.