Use of a live oocyst vaccine in broilers has become a widely accepted means of controlling coccidiosis. The commonly used live oocyst vaccines can beadministered to chicks at hatch using spray cabinets(Chapman et al., 2002; Williams, 2002), or to late stageembryos by in ovo injection (Williams, 2007). The livenonattenuated vaccine, Inovocox EM1, is recommendedfor the immunization of healthy broiler embryos between 18.0 and 19.0 doi for the prevention of coccidiosis. Therefore, the accuracy of injection, the movementof oocysts within the embryo, and their subsequent effects on broiler embryogenesis and hatching chick quality were investigated in eggs that were set and injected12 h apart (18.5 or 19.0 IAN) under the same incubation conditions