Chickens, infected with a small number of Campylobacter jejuni, ceased excreting C. jejuni in their feces 3 months after challenge, although mice shed the organism for 6 months or more. C. jejuni was excreted in the feces of 3-day-old chickens longer than in those of 5-week-old ones. Three-month-old chickens ceased to excrete the bacteria in the feces earlier than did 5-week-old ones. The minimum infectious dose of organisms depended on the age of chickens and strains used. C. jejuni was observed not only in the contents of the digestive tract but also in the spleen and the liver of infected chickens. Fecal excretion continued by serum agglutinin was developed to 1:80. This suggested that humoral antibodies developed in the chicken body might have no important effect on the fecal excretion of C. jejuni.