An oil-emulsion vaccine was prepared from phage type 4 Salmonella enteritidis to assess the potential protective efficacy of S. enteritidis vaccine and the effect of stress after vaccination. Hens were vaccinated at 14 and 18 weeks of age and challenged orally at 24 weeks of age with 10(6) or 10(3) cells of a homologous S. enteritidis strain. Pullets were vaccinated at 8 and 12 weeks of age and challenged with 10(9) cells. The O antibody titers of vaccinated hens rose quickly and were unchanged after challenge. S. enteritidis was isolated from cecal droppings of significantly fewer vaccinated hens than unvaccinated control hens for 6-21 days and 2-15 days after challenge with 10(6) and 10(3) cells, respectively. S. enteritidis was also isolated from livers and spleens of significantly fewer vaccinated pullets for 1 week. Vaccinated and control hens were equally affected by exposure to environmental stress, the result being that the shedding rate of S. enteritidis in cecal droppings increased equally in both groups.