SUMMARY In a survey for Cryptosporidial infection among commercial native and foreign breed chickens of different poultry markets in Ismailia city, the overall prevalence of Cryptosporidium sp. oocysts among the examined commercial chickens was 10.96%. The prevalence of Cryptosporidial infection in foreign fattening broilers aged 45-60 days (17.6%) was significantly higher than that reported among native semi-mature chickens aged 3-4 months (8.5%). However, there was no significant difference between Cryptosporidial positive rate of native layers (4%) and that obtained among foreign layers (2%. In general Cryptosporidial infection positive rate of commercial foreign breed chickens (13.2%) was significantly higher than that recorded among commercial native
breed ones (7%). Histological examination of the infected chicken intestines confirmed various stages of Cryptosporidium sp. attached to the epithelial cells of the small intestines. Current research indicates that intestinal Cryptosporidial infection occurs on a flock or premises and is more likely to occur in younger birds than older birds. These findings have considerable epidemiological and public health significance for the investigated area.