To explore the relative contribution that flagella and Salmonella invasion proteins make to the virulence of Salmonella enteritidis in poultry, 20-day-old chicks were challenged orally and by subcutaneous injection with wild-type strain SE-HCD, two non-flagellated mutants (fliC::Tn10 mutant and flhD::Tn10 mutant) and two Salmonella invasion protein insertion mutants (sipD and iacP). When injected subcutaneously, wild-type SE-HCD was the only strain to cause substantial mortality and morbidity and to grow well in organs. The flhD mutant of SE-HCD was invasive when given orally, whereas wild-type SE-HCD and the fliC mutant were significantly attenuated. Salmonella invasion protein mutants were not invasive by either route. These results suggest that temporary suppression of Class I regulators of flagellin biosynthesis may aid oral infection in poultry.