Male turkeys were infected with Eimeria adenoeides at approximately 15 or more days old. They received either a single inoculation or daily infections comprising a constant dose of oocytsts. The observed decrease in growth was largely due to a lower than normal intake of food. A comparison of single and multiple infections showed that the duration of the observed symptoms hardly differed in either case. Changes in certain blood parameters which occured during the course of the disease were similar to the changes seen in chickens with caecal coccidiosis. The persistence of these changes following repeated infections revealed the action of a parasite on digestive function which is not found in chickens infected with E. tenella. Modifications of the caecal bacterial flora were also observed (an increase in the populations of enterobacterial and anaerobes) during the course of the development of the parasitic disorder. Repeated infections prolonged the duration of this phenomenon. The similarity of those variations to those observed in the chicken with caecal coccidiosis suggests a fundamental role of some bacteria in the expression of the pathogenic potential of E. adenoeides.