Embryo transfer is a commonly performed surgical technique with applications in transgenic animal production, species re-derivation, assisted reproduction, and scientific research. In mice, protocols typically specify pairing recipient females with vasectomised males to induce a receptive uterine environment for embryo implantation. However, this induced receptive state, termed ‘pseudopregnancy’, is not always maintained until implantation occurs. We therefore evaluated the use of a well-characterised correlation between estrous state and exfoliative vaginal cytology to assess uterine receptivity immediately prior to embryo transfer. Eight to twelve week old virgin female CD1 mice (n=22) were paired overnight with vasectomised males. Successful mating was indicated by the presence of a vaginal plug the following morning. These dams underwent embryo transfer 3 days later with embryos obtained from superovulated four week old F1(C57BL/6 X CBA) females. Non-invasive vaginal lavage was conducted immediately prior to transfer. Dams were killed 6 days after transfer and the uterus collected for histological analysis. Embryo implantation rate in mice was 96% when quantitative cytological analysis of the lavage samples signified diestrus (n=6), whereas the implantation rate was <15% (n=16) when cytology signified other stages of estrous. This simple, quick, non-invasive measure of receptivity was found to be accurate and easily adopted, avoiding unnecessary surgery and subsequent culling of non-suitable recipients, while maximising the implantation potential of each recipient female.