Preimplantation embryos from mice and cattle were exposed to bluetongue virus in vitro to determine whether the virus would replicate in these early embryos and, if so, what pathologic consequences would ensue. A high proportion of zona pellucida-free, 2-cell embryos as well as morulae from mice and cattle became infected. The infection was rapidly cytopathic in embryos from both species. Indirect immunofluorescence was used to demonstrate accumultion of virus antigen in the blastomeres of these embryos. The zona pellucida of both murine and bovine embryos provided effective protection from virus present in culture fluid.