Background: The intracellular parasite Cryptosporidium parvum (C. parvum) is a causative agent of diarrhea in humans and potentially fatal in AIDS patients. The parasites develop in enterocytes and are transmitted mainly by the fecal-oral route. In developing countries, infections are more common in children and may be associated with malabsorption and malnutrition. Enterocytes are an active component of intestinal mucosal immunity and their resistance to infection can be mediated by more than one mechanism including responding to cytokine signals. IFN-γ activates various mechanisms in infected enterocytes to kill invading pathogens. In contrast, transforming growth factor β (TGF-β) is crucial in downregulating inflammation caused by the Th1 response. Aim of Study: This study aims to investigate the role of IFN-γ and TGF-β in host immunity against C. parvum infection. Methods: To determine the role of IFN- on the development of C. parvum in vitro, HT-29 monolayers were incubated for 24h with varying concentrations of IFN-. Following infection with C. parvum oocyst, the cells were re-incubated with cytokines for a further 24h before being fixed and stained with Giemsa. The parasites were then counted using a Zeiss Axioplan microscope at x1000 magnification with oil-immersion in 20 random fields across the diameter of the coverslip. Results: IFN- was found to have a marked inhibitory effect on C. parvum infection. The effect of IFN-γ was partially reversed by TGF-β, which produces a significant dose-dependent antagonist of IFN-γ activity. IFN-γ mediated its action by modification of intracellular Fe2+ concentration.