SYNOPSIS. Sporozoites ofEimeria tenellawere injected into the peritoneal cavity of normal chickens and chickens immunized againstE. tenella.In some experiments normal scrum and serum from resistant chickens were injected prior to the injection of sporozoites. After 15 or 30 minute periods of intraperitoneal incubation, exudates were harvested and the occurrence of intracellular sporozoites was determined.Only macrophages and degranulated granulocytes were observed to contain sporozoites. There was no significant difference between the number of macrophages obtained from normal chickens (normal macrophages) which contained sporozoites and the number of macrophages obtained from immune chickens (immune macrophages) which contained sporozoites. Significantly fewer immune macrophages treated with immune serum contained sporozoites than untreated normal or immune cells, normal macrophages treated with either serum, or immune macrophages treated with normal scrum.Sporozoites in untreated normal macrophages did not appear to be harmed by the intracellular environment, based on structural observations. The majority of sporozoites in macrophages from all other groups were difficult to distinguish within the cytoplasm and were visibly distorted.It is hypothesized that the presence of fewer infected macrophages in exudates of immune chickens and serum‐treated normal chickens was caused by an enhanced ability of these cells to destroy the parasite.Similar observations were noted in the case of sporozoites within degranulated granulocytes of experimental groups. The lack of understanding of the degranulation phenomenon makes it difficult to interpret these finding