Six-month-old cockerels and point-of-lay pullets were infected orally with S infantis (1 X 10(10). The cockerels were slaughtered at intervals up to 42 days, and the pullets slaughtered 20 weeks, after infection. Infection produced no clinical disease and minimal changes were observed at autopsy. Serological responses were transient, frequently absent three to six weeks after infection, no response at all being recorded in some birds. Faecal excretion was observed most frequently during the early stages of infection. There was no evidence of egg transmission.