The aim of this investigation was to detect and examine the distribution of the CD3-T lymphocyte cell population of the Bursa Fabricius in chickens experimentally infected with Eimeria tenella. Slices of archived samples of Bursa were examined using the of direct peroxidase (DP) method. CD3-T lymphocytes were detected with human anti-CD3 antibody. They were localized in the cortico-medullary layer of Bursa follicles in uninfected chickens. The immunoreactivity of bursal tissue was directly correlated with the stage of development of E. tenella, with the highest intensity in the epithelium of the folds and in the layers of follicles between 3 and 5 days after the infection, predominantly in the cortico-medullary layer of the follicles. These results demonstrate the existence of an early cellular immunological response to infection with E. tenella.