The pathogenicity of Leucocytozoon caulleryi against specific-pathogen-free laying hens was investigated. Many large schizonts (second-generation schizonts) of L. caulleryi were seen in the ovary and oviducts of chickens. Edema and pressure atrophy of the adjacent tissues were associated with these schizonts. The eggshell-secreting portion of the uterus exhibited the most severe damage in the oviduct. This experiment reconfirms that L. caulleryi may stop egg production in laying hens, presumably as a result of damage to ovaries and oviducts.