We examined the time course and histological localisation of the developmental stages of Eimeria colchici. The prepatent period in the caeca of pheasants was 6 days. The patent period began on day 7 post-infection (p.i.) and ended on day 11 p.i. with peak production of oocysts on days 8-9. The peripheral blood lymphocytes of pheasant chicks showed a significant increase in proliferation to E. colchici antigen from day 5 p.i., with peak on day 14 p.i. The metabolic activity (respiratory burst) of heterophils increased on days 3, 4 and 14 p.i. The total number of peripheral blood leukocytes and lymphocytes in the infected pheasant chicks had increased by day 2 p.i. and reached a maximum on day 4 of the experiment. Days 5 and 6 p.i. were characterised by a drop in the number of these cells.